"you don't want to attract the attention of somebody who is already belligerent and vile."

I would rather these folks/comments are flushed out (the OP claims that someone belligerent and vile are getting a lot of upvotes, which seems strange to me - I don't doubt that mean people post on HN but if they are getting tonnes of upvotes (vs being downvoted or flagged) it would be really nice to see examples), but I appreciate that other people have different approaches to confrontation.

The problem is that then it is very hard to take a claim like "general uptick in mean spirited comments" seriously. A asking for evidence of any claim is valid in any discussion.

Heck if anyone wants to point these out but don't want to be seen doing it, just create a throw away account and use that?

I would agree that there is no reason not to single out those who are constantly belligerent and vile. When these individuals are easy to identify they are often isolate from a group and do not end up causing many problems. However that is probably not the case that causes the most problems.

The case that I have seen cause the most problems are the people who are normally ok but are belligerent and vile with a specific topic and or individual. This hypothetical individual is normally a productive part of the community and may not deserve to singled out. I would not out such a person unless I had good reason to believe that that they would be treated rationally and that the community would only see it as an opportunity to help said hypothetical individual to become more rational.