One distinction I don't see people making enough is the difference between reason and rationale. Reason is the process of using one's mental faculties to assess a situation and come to a conclusion about what must be done. Rationale is using one's mental faculties to come up with justification for what one has already decided to do. This is an important distinction to keep in mind.
To pick a vaguely topical example, if you're arguing with someone who's very strongly in favor of socialized medicine for reasons such as peer pressure, arguing with their stated reasons for instituting socialized medicine is futile in many ways. Arguing with someone's rationale is pointless, because they spring up like weeds. This is, of course, only assuming that your goal is to convince that person that they're wrong. Arguing with that person in a public forum with the goal of convincing the audience is often worthwhile.