Major social revolutions on questions of morality are rare, and we appear to have lived through one quite recently - the transition to widespread acceptance of gay marriage. As such, it provides a natural laboratory for the ideas Jonathan Haidt has described in his book, The Righteous Mind. Gay marriage presents a fundamental collision between the two pillars of liberal morality - care and fairness - and a third fundamental moral module which is much more important to conservatives - the purity/sanctity module.
Purity/sanctity can be considered to be concerned mostly with societal "rules of the road," regulations which have an element of arbitrariness to them, like the rule for driving on the right side of the road (in most countries) but are necessary for the smooth functioning of society. Such rules are given moral weight by embedding them in a moral/religious matrix.
One effect of having read The Righteous Mind is that I can now articulate the conservative arguments against, say, gay marriage, better than I have heard them do so. The most fundamental conservative argument is that morality is a crucial but vulnerable element of what is required for us to live together in groups, and tinkering with crucial elements of it is dangerous. No element of social morality is more crucial than marriage, so tinkering with that is pretty momentous and potentially disastrous.
The liberal rejoinder, I suppose, is that we have been tinkering with marriage for a long time - true enough, and whom does it harm, anyway. America, and much of the developed world, seems to have concluded that the liberal argument is more persuasive.