Sure, but if he can't find a group in person that will validate and amplify his views and also can't find such online, he will probably remain some run-of-the-mill uncouth jackass without feeling so strongly about it that shooting up a mall seems like a good idea he should totally act upon.
There have been studies. Radicalization is generally the product of a social environment that magnifies certain views and actively encourages people to become more extreme.
Sure, the human has to physically exist before they can become radicalized. I don’t really follow the point here. It’s still important to figure out where the actual radicalization happens.
The roots are firmly in the meatspace.
The seed was planted well before he know what 8chan was.