Okay, I agree with that, particularly that we should attack policies, not people. I think there are cases where it is useful to generalize groups that don't have outwardly-stated ideologies (for example, when describing the political leanings of reporters for a given newspaper, or lobbyists' agendas) - with the critical distinction that these generalizations should not be done as a value judgments, but rather as observed trends of behavior for the purposes of rooting out possible effect of biases on information coming from those groups. In the case of reddit and sexism, therefore, I think it would be fair to say that language and behavior that objectifies women tends to be upvoted highly and given more weight by the community than criticism of such behavior, in at least the default subreddits.
Well-explained. It seems that you're saying that it's sometimes acceptable to infer policies and ideologies from the collective behaviour as a group. And on reflection, I agree. My real concern, I think, is that judgements like this, made from the outside, serve only to further polarise the behaviour. For example, describing Reddit as sexist, as an outsider, has the effect of removing Redditors who do not want to be considered sexist (probably because they're not), which in turn increases the net-sexism of the community. Labelling a community from the outside may help to shun them from wider society, but it doesn't help to fix them: that has to happen from within. (not that I know the best strategy to do that with Reddit and sexism, though, although I try to do my part to downvote/criticise/educate where appropriate)