As you've observed: saying than an entire community is prejudiced is prejudiced (e.g. "Redditors are sexist."). We all do better, as a species, when we focus on our own experiences. E.g. "When I went to Reddit, the comments by many of the people there made me feel that they were being sexist towards me." The latter

(a) focuses on the individual, rather than sterotyping the group, which helps to defuse discrimination, rather than fuelling it, and

(b) focuses on the experience, which is important in allowing others to empathise with us, which in turn is valuable in breaking down discrimination

Even in the developed world, there still remains a great deal of legal and political sexism (the pay gap, career choices, maternity/paternity leave), as well as an even larger amount of social sexism (mens and womens roles, boys and girls toys, etc.). We've come a long way, but there's a long way still to go. Still: we're moving in the right direction, and it's okay to relax a little about it all.

But when it comes down to toilet seats? Man, that's getting silly. You're going to wash your hands when you're done anyway, right? So touching a probably-pretty-clean-actually toilet seat for a few seconds isn't going to hurt you. You leave it whichever way you like; I'll leave it whichever way I like; and we'll both be nice to one another... it'll probably work out.

tl;dr: Be nice to one another.