I'm late to the discussion. Regarding downvotes--imo that's asking for trouble. People can vote down for any number of reasons, some valid, others not. At any rate, it's making negativity public. People differ as well as to how likely they are to use like or dislike buttons. I don't like 'like' buttons, so I don't use them, but it doesn't mean I don't like a particular post.
Maybe I'm not visiting enough of the subforums, but I'm not seeing contentiousness on the rise. If it does, the mods should be the ones deciding when it's progressed from brisk discussion to argument to contentiousness. A forum needs to have room for disagreement. I know I have learned a lot over the years from the back and forth of people with differing opinions/facts.
For posters whose posts I've found from long experience to not be interesting to me, I do a mental Block/Ignore and just don't read them.