In my experience, downvotes do little but encourage dog-piling and echo chambers. I have a few accounts on instances that disabled downvotes, and few that enabled them. The difference is very clear. The instances that disabled them have noticeably more rich and diverse discussion, with users being less afraid to disagree with each other and have proper debates.

The instances that have them enabled vary a bit, but I noticed a pattern that certainly reminds me of The Hard R: Most comments on a popular and highly upvoted post are basically people agreeing with the post over and over again with different words, and then there a few comments that actually disagree, but you'll have a hard time seeing them because they were downvoted into oblivion. This isn't always the case, certainly not as much as the other place (at least not yet) but I have already noticed it happen.