Youtube also has 'dislikes'. There are a few other forums not worth mentioning that use a downvote system as well.

I believe if platforms like Facebook and Twitter normalized downvotes long ago, there would be far less online social media heat. They can't downvote on Facebook, but the toxic element is still there, with words. Some spend days arguing, for nothing. "Likes" are a form of reward. They move words up and down. In the response section you'll often find trolls. If people think downvotes are toxic, they need to go look at how truly toxic those other places are, then maybe start comparing.