On the one hand you've got specifically American attitudes - ie that constitutionally-protected freedom of speech applies even to privately-owned websites to which individuals have access, ie "freedom of speech" means "I can go on some website and say what I like, ideally without any consequences" - and on the other hand you've got the corporate/business desires - usually to make money (in the case of websites, by selling advertising, because charging for access isn't going to work) and minimise costs.
Those two things can't easily co-exist; at best you build a good community initially and volunteer mods help keep things more or less ticking over (while costing nothing and providing a reasonable answer to the whole "legal liability if we don't respond to complaints/illegal content pretty quickly"). The problem is, being a mod can limit how much you get to participate in the community and can lead to burnout - so unless your management/leadership are very astute in their understanding of the community, conflicts can happen easily between the punters and management.
Personally, I think that the lack of willingness to enforce higher standards of discussion is what makes a lot of discussion sites unpleasant from the outside. But that would limit the potential appeal to the "asshole tireless rebutter" contingent of the potential audience, so it usually won't fly on sites that need high hit-counts to drive advertising rates...