The discussion there may be "civil", but it's not healthy.
Truly healthy discussion inherently involves people expressing ideas and opinions that may be provocative. Some people very likely will be offended by these ideas. Some people will get angry. Some people won't believe what they're reading or hearing. But those are all good things. They indicate that there is a wide variety of thought going on.
Communities that are kept "civil" through the use of excessive moderation, for example, thrive only in a very superficial way. Given enough time, intellectual inbreeding happens, where the vast majority of participants adhere to a very strict dogma. Any real contemplation is quickly extinguished. The end result is a very bland type of thought, devoid of real substance. It's not truly healthy, even though it might look good on the surface.
Very lucid and interesting post. However, if you look at other communities like Slashdot, a level of civility is enforced by the community, without necessarily stifling unpopular or dissenting viewpoints (at least once upon a time). It becomes a matter of filtering out inflammatory posts ("trolls"), and that will ultimately depend on the tastes and preferences of the community at large.
Don't get me wrong, the contributors to those subreddits are amazing, but what makes those subreddits work the way they do is the strict moderation. Unsupported posts, memes, etc. are immediately k.o.s. and I believe that's what keeps the quality contributors from leaving.
The most exposed among the high-quality "ask" subreddits may be /r/askscience. There you will typically find that whole swathes of subthreads have been deleted by the moderators. There are lots of civil, high-quality contributors, to be sure; but it's the moderators that ensure that it stays civil and focused.
