I think this is the crux of the issue with this user. (I’m assuming they’re just a user and not a moderator or admin.) Circumstances never warrant speaking harshly to people on a software forum, in my opinion. This is sometimes a hard rule to live by, I break it myself on occasion … and do my best to apologize when I do without covering it up. Even corrective actions such as warnings and bannings should be delivered with respect and care, even if it isn’t deserved in some people’s opinion.
Only a moderator or admin should be making the decision of who should go and who should stay … and only then when they are calmly, logically and consciously making the decision. Not some general member of the community who likes abusing people. Because that is what is happening, this member of your community is deciding that they will abuse people until they leave or conform to their rules, not the forum’s rules. In ten years, you’ve most likely lost at least a few people that could have replaced this troublemaker’s expertise and not had to use your forum as an outlet for their frustrations and pent-up rage.
I’m currently crafting a conference talk on my experiences as a moderator on a software forum. One of the headings is “The Community is More Important Than You” (meaning the moderator). That goes for any single member of a forum as well. If a forum member, no matter their status or privilege, is damaging the community, they need to go.