Edit-I don’t know the best way to exit this problem. But I’d probably start with telling the disparate groups that their positions are not so abnormal and maybe they would be happier focusing on other things-like hobbies that require time offline. Have your “incel” days and have days you force yourself to do something, anything else than think that.
Healthcare for mental health is still very much underdeveloped, especially when the patient is male. It is just easier to blame the individual.
The analogy breaks down when you start to try and think of what our "vaccine" might be, though perhaps education can be a rough proxy. It's also possible there's nothing we can do, and we've reached a spread that is incurable...
(1) https://daily.jstor.org/an-affordable-radio-brought-nazi-pro...
I dispute that causation. Mass murderers are extreme outliers that usually have identifiable mental problems, and I would say the primary cause of their behavior is those mental problems, not whatever particular thing they say triggered them. Also, even if you did show that a certain ideological group was significantly overrepresented among mass murderers, you would have to rule out the other methods of causation (e.g. this guy is a loner because of various problems, and he joined this group of loners because they welcomed him—doesn't mean the group caused him to go commit the murders, and in fact it's conceivable that being in the group reduces the likelihood of the potential murderers actually going and doing it).