The separate downvote Mana was the "missing link" I think. Because pre-HF21/22 had to choose between either positive rewarding (including curation rewards) and negative rewarding (without any curation rewards, and hindering the ability to upvote something else), as a result downvotes were relatively rare. When downvotes are rare and somebody does receive one, they can easily be offended, retaliate or leave, and/or take things personal.
But if you look at Youtube for example, even top quality videos get downvotes. Downvoting there is an integral part of the platform culture and it's about the ratio up/down that functions as a content quality metric.
Post HF21/22 downvoting as a separate tool, where an occasional downvote does not hinder the ability to upvote good content and hence the need to choose between downvoting X over upvoting Y is absent, it's everyone's "duty" to help disincentivise posting and upvoting utter junk. And as more and more people, accounts large and small, utilize their downvotes, it might also become an integral part of culture on Steem as well.