Conservatism is by and large a political term and conservatives are usually defined by their actions, defined politically by who they vote for. So if for instance someone disagrees with a policy of SSM, it may be a cognitive process that does not differ from someone who supports it. The determination may be effected by different circumstances or experiences but certainly not by a strict correlation to a willingness to weigh up pros and cons. If some psychologists determine that conservatives are less likely to make rational decisions then that would be a very skewed analysis. Rationality is also subjective by nature!
