Opinions that are voiced less often than people hold them, for obvious structural reasons:

“Actually I like doing that thing you called contemptible or harmful, and I want to keep doing it”

“I like life and the world pretty much as it is”

“I have nobody to blame but myself for my problems and they’re pretty embarrassing”

“I believe firmly in something that’s too obvious/banal/boring to mention explicitly in my social environment (even if it’s controversial elsewhere)”

“This topic is disgusting/toxic and everyone who talks about it is making things worse”

“I actually know what I am talking about and you don’t, but I have a busy life and access to lots of confidential information and so I cannot really communicate my knowledge in public”

“I find this so confusing/boring that my brain just bounces off it”

“I consider this too stupid to dignify with a response”

“It’s not that you’re wrong, it’s that all your concepts and emphases and methods of thinking seem subtly off, or disconnected from what I see as important, such that I can’t even begin to formulate a reply”

“I’d argue with you, but I expect you to be thin-skinned, angry, or even vindictive if I give pushback, so I better shut up”

“I’m hurt, troubled, or offended by what you said, but I’ll look weak if I just say that directly”

“I like you, and I wish you were right, so I don’t want to publicly disagree or doubt your project’s viability, but…nah, I don’t buy this”