16 year old boys have always been easy-to-radicalize idiots, but most grow out of that and into mature adults. I should know, I was a 16 year old boy once and so were many of us here. 16 year old boys are fucking idiots, and writing them off for bad political views is how you let those bad political views fester and become permanent
Cool, now go be a teacher in line of fire where these little radicals go to school. Make the difference yourself since you argue they should be allowed to be there but not that their peers should be allowed safety.
Expelling doesn't mean cutting off education. It means removal from that specific school for a time.
There are alternative schools specifically for these cases. So these little Nazis will end up shunted over there if they are not allowed to return to their original school.