Serial killer groupies always existed. Except for the Manson Family, we tended not to pay attention to them.
Historically serial killers and mass murderers have always had their groupies. Explaining that phenomenon requires four psychiatrists and a Bell Jar. Human beings have deep wells of depravity and there is a very specific type of mind that is attracted to a murderer. The phenomenon of teenage girls who fall in love with serial killers and liberal societies who fall in love with Islam is not so different.
Murderers always got plenty of fan mail, but the modern American Idol and Infowars twist on the phenomenon is that it makes the fans famous and the fans use their fame to sell more conspiracy theories. Both are toxic.
We live in a society where fame is the biggest intoxicant for many teenagers. The one thing you really don't want to do is reward a phenomenon this toxic with what it craves... fame.
Talking about the Holmies or the Free Jafar crowd increases their numbers. People this screwed up are completely immune to shame or negative feedback. On some level they crave it as the next best thing to what their "heroes" did. They don't have the guts to go out and kill, but they have their "Squeaky Fromme" moments by outraging the victims.
Serial killer groupies always existed. Except for the Manson Family, we tended not to pay attention to them. And part of the reason for that is because people this repugnant are not worth paying attention to. They have no power, except the power to outrage and disgust. Deny them that power and they are no different than every other group of creeps hiding in the shadows. Give them that power and teenage girls will be drawn in for various misanthropic reasons.
Our society is full of rocks under which dark things hide. There's a judgement call about which rocks to turn over, but it's best to remember that the number of rocks and things under them these days is nearly infinite.