#1 and #2 cause strong negative backlash. As you would learn from marketing theory, a user that you have personally screwed with will likely cause 20x more damage to your brand than your best users improve it. #3 Locks out a lot of useful expertise. For sure, HN could use a lot more knowledge about programming. So far, this site has attracted lots of people who want to learn but much less so people who already know a lot and have wide experience. We still very much need to be inviting to the latter.
Another point that very knowledgeable people are very opinionated, stubborn, and generally assholes. Linus Torvalds is the stereotypical example. This is not to excusing the behavior, but the correlation exists and we will all have to try not to get so offended and ban people like immature children.
If you try to hold onto the past forever instead of trying to improve then you will fail.
I hope this was useful.