I will agree with you on this. I think the moderation policies should be clearly delineated or they don't really exist. A law is not much of a law if it's unequally applied.
You bring up an interesting point about "discovery" of view points you want to hear about, especially when you consider the foundation of the Internet as a platform: search engines. One problematic example I can think of off the top of my head is the "anti-vaxx" movement, which may be promoting a message that some people want to hear but at what cost to their children or the larger society who are subject to those parents' whims or beliefs? Very different than me discovering there are other people out there on the internet who are disturbed by the Garfield comic and want to joke about the existential horror of a cartoon cat and his owner.
I can't say that I have an easy answer for the issue of the harmful effects of a platform on the societies its users are members of. Or even determining what is harmful (or not).