It's not a lost cause. Most of these destructive effects are unintentional. Indeed they don't feel destructive at all, they feel like standing up for what's right. That is why people post and upvote them. And in fact they are standing up for what's right, but unfortunately doing it in an way that is destructive of the community and thus does more harm than good.

It's possible to recognize this pattern and choose to change it into one that has positive side effects instead of negative ones. Many HN users have done so. I had a long process to go through myself.

As for the culture of the forum having shifted recently, it's society at large that has become more vitriolic. This is not unique to HN, nor can we expect to be immune from macro trends. We need to assess this accurately to have good options for reacting. If a boat is lurching because of a stormy sea, the problem is not in the boat. Unless the sea smashes the boat altogether.