This is inspired by Ross Douthat's blog post today in the NY Times. The debate he is writing about is quite interesting, it is worth following through to the various links he posts.
The thread I want to pull out however, is Douthat's last point where he criticizes Matt Yglesias. I think this most clearly shows conservatism's problem, they're still thinking in terms of first principles and stuck in the 20th century. Ygelsias mentions a couple of groups that show where the rough grouping of the left has changed greatly, the feminists and the "green types." While neither is a field that I'm extremely well acquainted with I'm familiar enough with the concepts to know that both groups represent some of the new thinking that is challenging older ideologies. Feminism especially has opened up ideas of the force of norms and identity in shaping economic and political reality, something that isn't exactly dealt with in the first principles (however you want to define these) of either conservatism or liberalism.
This is where the two ideologies seem to me to differ the most. I haven't thought long and hard about the various strands of thought that make up the first principles of modern liberalism vs. conservatism so I'll take Douthat at his word that conservatism has more ideological diversity from first principles. However, I feel that liberalism has more effectively (if far, far from completely) engaged with the critical work that is questioning the largely 19th century assumptions that these ideologies rest upon. The principal areas that I feel have changed are the rejection of determinism, the role of culture in shaping both the economy and society, and the changing role of the state. While these concepts do of course influence conservatism as well (the McArdle article Douthat links to discusses privilege, which I would consider part of the cultural critique, and Samuel Huntigton's "Clash of Civilizations" is another cultural critique that has been influential on both the right and left) the political left seems to have done a better job introducing them into policy. Some of these are of course old ideas re-branded and altered by the new concepts as opposed to new positions made wholly from new concepts, the environmental movement, as an example, has elements pushing both for more regulation as well as for ideas having to do with expanded notions of the role of the market and the states role in creating this. For instance, cap and trade, or movements to create some form of property right to manage fish stocks (of course some conservatives are involved in both these ideas, I see the critique as being a critique of both liberal and conservative ideologies, I just believe liberals have more effectively incorporated these ideas) rely on a more complex relation between the state and markets and show the idea of a continued evolution of both the concept of the state and the market.
Liberalism is also more effectively trying to deal with the shifting nature of expectations on the state and market. For instance, the changing role of women as older ideas decline and the increase in mobility which has affected family structure (how many people take care of their aging parents till death in their own home, and live close enough this is even thinkable, today, how many did in the 19th century?) requires new institutions to deal with these cultural changes in the absence of other traditional institutions to fill a badly needed role. Previously many needs were met by institutions outside the state, read Adam Smith's section in "The Wealth of Nations" (p. 152 of my edition, incidentally, he also gives an argument against decentralization of social services due to each locality wanting to avoid paying for the poor which restricts mobility, obviously these are anachronistic terms for his argument) on the poor laws that needed to be put in place after the destruction of monasteries for a very early example of how the responsibilities of the state can change due to alterations in other non-state institutions. Security previously provided by non-state mediating institutions needs to be replaced somehow, often, especially due to modern mobility, the state is the only entity capable of this.
Several of these concepts also seem like they'd be particularly difficult for conservatives to grapple with, at least if I'm reading their ideology correctly. For example, as many fields increasingly reject a deterministic viewpoint and instead see development as a more complex and ongoing process (meaning that this is not the "end of history" and that modern ideas about markets and government are not the culmination of some long historical process but merely a single point in a system of continuous change, a particularly difficult concept if you idolize the late 19th century) it makes it difficult to both accept this narrative and reject the notion of the Constitution as living document as a distinctly liberal view, as one blogger linked to by Douthat does. I may not fully understand the differences between the Constitution as living document as a legal doctrine and the exact interpretation the conservatives favor as a legal doctrine but I think it should be obvious that since the understanding of certain basic concepts have changed, such as the notion of the people, property, and the individual all of which were obviously somewhat different concepts in a time where representation could be granted to 3/5ths of a person and the people holding such a person as property could take advantage of the representation granted to such a person. This is not to say that similar disenfranchisement doesn't happen today, illegal immigrants for example, but it will be very difficult for anyone to convince me that someone operating with modern concepts of these things would even think that representation of such a person should be fractional. Some of the writers of the Constitution were certainly troubled by this, and I do believe they saw that some of these ideas would require changes later on, but I believe it is easier to think that they retained a more corporate sense of political identity than we currently function with (also the lack of representation for women is a notable example of this corporatist attitude) and if these basic concepts have changed in meaning in the past 200 years than how could the Constitution be anything but a living document? The nature of the state, as well as other corporate institutions, such as corporations or the diverse entities known as NGO's and international organizations, is under continual evolution and policies must be updated to reflect changing ideas.
Another aspect that modern conservatism seems to have problems with is its myopic obsession with the state. The divide between public and private seems increasingly forced, it works well enough as an abstraction but when people are dependent on their company for many social services, most obviously health care (though this originated somewhat inadvertently from state action) but increasingly also pensions, childcare, and in a few cases even relatively trivial things such as fitness programs, the role of various institutions is blurring. Much of the growth of the state can also be conceptualized as the state needing to step in as modernization destroyed older institutions that formerly filled functions the state now does. Something that often strikes me is that before the automobile local neighborhoods had a much greater ability to conduct community action and self-help, people who had only the stores in walking distance and saw each other on the trains naturally would meet, find out about problems, and find ways to band together and help out (this topic could be a long aside, I have a lot of thoughts of how the auto has had huge unintended impacts on our culture and changed the way we relate to one another, I may take this up in another blog post since this goes far off topic). This has become tougher as we've become more mobile necessitating the construction of ways of finding information and assistance without relying on our neighborhood, few members of which the average individual knows any more. There is currently no institution other than the state capable of this.
I wouldn't disagree that this is probably not a good thing but current institutions allow no other solution that would have widespread legitimacy on some of these issues. Trying to push things into the private sector fails because the current private sector isn't well structured to address general social concerns. Power is too concentrated in the private sector, even in non-profits upper management tends to have much greater compensation and authority. For people to buy into an institution aside from the state providing social services we would need a less authoritarian structure, existing shareholder voting or other means of consulting stakeholders are currently not developed enough or well established enough to replace even the limited control people feel the have on the state through voting. Personally, I believe the growth of the state will be temporary, eventually a better means of spinning off some of the duties of the state, social security and health care perhaps, will be found and the state will be reduced in size, this is in the future and not a good potential guide to current policy of course. However, I think the current focus by conservatives on the state is a weakness since the state seems less important and the ways authority is distributed more complex than that which makes a simple public/private divide work in theory. Historically, the relationship between the duties the state had and other political and social institutions was far more complex (see Wilson's "The Thirty Years War" for an example) and I think the trajectory is for the relationship to grow in complexity in the future. Focusing on the state (and taxes) as a problem seems increasingly quaint in the complex world of today and for conservatives to continue to focus on it will make them seem less and less relevant until they develop a more nuanced understanding of it. It just doesn't resonate the way it did when there was a Cold War on and the state politics between the two super powers dominated political thinking.
I still have a few thoughts clattering around my head on this and will continue this later. Please share any thoughts and criticisms you have on it to develop more fully later. To bring it back around to the beginning, I think what Douthat is missing in his idea that Conservatives are as, or more, diverse intellectually than liberalism, is that liberalism has begun to adopt many modern critiques of the basis behind both ideologies. Conservatives are wrong to dismiss these ideas as "liberal," they are not intrinsically so though political liberals do seem to have done more with these ideas than conservatives have. Continuing to dismiss these new, critical (I will willingly admit none of these criticisms have yet advanced to a productive new paradigm, they have simply shown integral flaws in old ideas) ideas weakens conservatism, to address the new problems society is facing as it continues to evolve requires questioning old assumptions and ideas to deal with newer problems. Treating them as variations of old ideas misses the logic behind these new ideas, they really are pointing in a different direction of development from older liberal concepts.