Eh, it's just the squeaky wheels, like it is anywhere. I find that people are much more likely to speak out (or up/down vote) in support of something they also do that they feel vaguely guilty for, possibly in an effort to assuage their guilt be explaining themselves and looking for people to tell them it's okay, than people are to condemn others, depending on the acceptableness of what's being discussed.

I think most people don't want to come across as puritanical hard-asses, so either keep quiet or are not as forceful in their criticisms and condemnations in a public forums like this with lots of different subgroups. That may make it seems like people are generally accepting of a behavior when they're not.

Importantly, I think this isn't limited to online forums, but it is lessened when there's more conformity in group discussion which is easier when it's smaller. That has it's own dangers though, such as being much more accepting of problematic behavior because the group is all similar in a way that makes it acceptable.

I think the solution is to see it for what it really is, and just realize what you see isn't always representative of the norm.