Every once in a while I'll be minding my own business and a thought pops in my head with crystal clarity. Usually I live in this gray cloud of indistinct and nebulous thoughts so when something like this happens it is refreshing. The circumstances that clarified this for me are not important (I can't remember them anyway) but what I realized is that while I find a lot of enjoyment in having a spirited discussion with people that think differently than I do, the religiously faithful and the willfully ignorant are two types of people that I find it impossible to have any sort of meaningful difference in opinion with.
The very definition of faith doesn't lend itself to critical thinking. On part of having faith is believing in something despite evidence to the contrary. From my point of view, a lot of the tenants of different faiths are self-contradicting and not always consistent. That people find hope and reason for being in faith is a good thing in my opinion. I just don't see the point in engaging them in a debate about it.
The willfully ignorant are by the most frustrating people to have any sort of disagreement with. Like the faithful, critical thinking is not something held in high esteem. What I mean by willfully ignorant are people that believe something for primarily ideological reasons despite the overwhelming evidence to the contrary. For example, that Obama is a socialist/marxist/facist and/or was not born in the United States. It is like arguing with a brick trying to challenge that belief. Another one that burns me is global warming denialism.
What it boils down to is this: Challenging assumptions/beliefs is healthy. I like having a debate with someone that doesn't hold on to an opinion from an ideological or theological position but from a well information opinion. I think well informed people can draw different conclusions and have honest disagreements. Those conversations are very enlightening and enjoyable. As for the others, there is still value in understanding their point of view. There just isn't any value in challenging it.