It's funny you should mention a bell curve. The other day, while thinking about this, I pictured society as a bell curve progressing over time. What was "perfectly normal societal behavior" two generations ago winds up being "highly racist comments" nowadays. One of the problems with these fringe groups is that they see the bell curve passing them by and long for the days when they were in the middle of the curve. (Whether they ever actually would have been in the middle or whether they are glamorizing the past and putting themselves in the middle is another story.) The more the bell curve passes them by, the more desperate they get to pull it back and the more they are willing to resort to behavior that shocks the current "normal society."
Sadly, the long tail of the bell curve probably means that these people will be around for quite awhile, getting more and more desperate to get society to conform to their view of what it should be.