I agree very much with your lines of thought. It is indeed a problem with Steem that it does not promote discussions, but then again, it's probably not worse than the alternatives ...

• Steem - currently it seems most profitable to agree with people and eventually ignore posts if one disagrees rather than start an argument. It's at one hand a sad situation. At the other hand, it is a good thing that the incentives are not aligned with the "trench warfare mentality". It takes a bit of time and effort, but it is a useful skill to write "I disagree strongly with this, and I believe you're bonkers" in a polite way, supported by proper arguments.

• Facebook - one is efficiently shielded from opinions from those one disagrees with. It's very bad, as extremists get no counter arguments, it's easy to underestimate the amount of people that disagree with you, and as people actually gets surprised when they find people having opposing points of view out there.

• Reddit - this was one of the foremost arenas of the "Bitcoin schism", the trench warfare between the "big blockers" and the "small blockers" (short version: neither the "small blockers" nor the "big blockers" wanted any kind of compromise (I think SegWit2X wasn't that bad), and the "small blockers" won the propaganda war, the definition of "bitcoin" and the market cap). It was horrible to see how the two groups of people were only reinforcing each others view and generating hatred.