Marvel in particular has always shilled liberal views. You're only noticing it now because you're an adult and you don't side with left social politics. The X-Men have been about social justice since the beginning, with mutants representing whatever identity group the writers want to commentate on. Not saying it's a good or bad thing-- I'm just pointing out that it's nothing new.
Comics *are* nose-diving in sales, though, along with most other print-comics. This is mostly because of technology. Why buy a bunch of pieces of paper stapled together every few weeks when webcomics are free and generally update more frequently? Plus, webcomics don't suffer from the "too many cooks spoil the broth" issue that comics usually do. A webcomic can be one person's creative vision, which, yes, opens the gates for lots of garbage, but also lots of cool things that wouldn't ordinarily make it to print.
Back to 4chan, though: I think a big part of the site's decline has to do with peoples' gradual change in attitude towards the internet and anonymity. People just don't want to be anonymous anymore unless they have either really low self esteem or some really unpopular shit to say. They just value their identity and the possibility of making friends too much. Plus, image boards' hostile attitudes towards newcomers and outdated structure means that they're not generally acquiring new users, just retaining old ones (which are gradually falling away). The smaller and more isolated an online community is, the more bizarre and exteme it gets. This is only amplified by the anonymity, because people can say whatever batshit things they want with accountability.
www.dailymail.co.uk
