Sweden has a reality TV show whit that very premise and it is called trollhunters. They choose a hate comment and then proceed to locate and confront the author. When done they also sometimes help the target of the hate, by example helping them filling a police report.

The show is followed with vigilantist justice as the people they locate usually end up receiving a lot of harassment from the public, and the benefit of making examples of people has not had any effect in decreasing hate messages online.

An interesting side note is that when you actually go after hate messages online, the gender stereotype of young male start to melt and you get a new stereotype. It is people with a lot of free time and who feel ignored by society. A typical example is thus middle age women.

However turning that hate towards going on a killing spree is unlikely for a middle age woman even if they say things like "someone should go down there and kill everyone", so there is a high rate of noise-to-massacre.

A lot of people who feel powerless use very strong language precisely because they feel like nothing they do matters. They often don't really mean it literally and wouldn't say it if they actually felt like anyone listened to anything they said.

They basically exaggerate their real desire, hoping that if they express their feelings strongly enough, it might lead to some very small action because their experience is that they are mostly not taken seriously and what they say mostly makes no impact. This is probably true of a lot of middle aged women.

I don't approve of the vigilante model, it just increases the general animosity in society. I'd rather there be public prosecutions of violence-advocating speech through the legal process.