Because young men have problems that aren't taken seriously. Then someone like Tate comes along and (quite literally) sells the "solution."
If a cult leader can swoop in and radicalise a whole lot of people, then there is an unaddressed or ignored problem going on. This is the kind of way someone like Hitler got so much support.
People who are educated, and live secure, fulfilling lives would be able to see Tate for the twat he is.