The premise is so flawed, especially the groups the author labels “right wing” in order to even have a premise as to be mind numbing.
The “ice burg” theory seems to assert that, even though we labeled every violent act we could as “right wing”, there still isn't much to foam at the mouth about. But that is because most of those right wingers are doing evil, violent stuff under the radar so there is no data to support the theory. Which proves they are out there, and really, REALLY dangerous.
The “ice berg theory” is a PC way of saying, “Since we can’t find the few lone nuts in time, we’ll just have to attack the entire larger group.”