Comment by Austiiiiii

In addition to the "gamified" aspect, the votes allow special interests to trivially control the perceived public opinion on an extremely broad scale. Opinions with downvotes are perceived as unpopular, and this has a chilling effect on free discussion.

A real person who expresses an idea and gets downvoted by a passing Russian propaganda bot may see the vote (and subsequent Reddit weighting algorithm fuckery that turns the one well-timed vote into 10 votes, which a lot of people aren't aware of) and feel ridiculed, which will discourage that person from expressing the same idea in the future.

Other people who see the same post with X downvotes will take note that that idea is unpopular, and may unconsciously realign their own views on the idea to fit what appears to be the prevailing opinion.

And of course crappy old forums have the other advantage of not having any single standard registration process or API that can be exploited by bots en masse. That's not going to keep them out entirely, but it drastically increases the logistical cost.