reddit has both moderation and curated content in the form of subreddits, and on Twitter you choose who else you engage with, it doesn't have to be strangers. Insofar as anyone here are also strangers.compare Reddit or Twitter is more akin to shouting your opinion at strangers on a street corner
Social media does incentivise interactions in ways that can turn sour (for "engagement" as they often put it) but it's funny how much they seem to be misunderstood. A well-moderated subreddit works as well as any forum. Twitter is only shouting at strangers if you a) choose to shout and b) do so at strangers
(Twitter would be a good study of toxicity promoted by the business model though - I believe studies have even been done)