"The only example that I know of, where downvotes exist is Reddit. However, on reddit you're only "losing" visibility & possible karma, which in comparison to the real currency STEEM is more than worthless."

I could argue the exact opposite.

Combined desktop and mobile visits to Reddit.com from February 2018 to July 2019 (in millions):

Source: https://www.statista.com/statistics/443332/reddit-monthly-visitors/