Rep. Richardson raises a crucial point about limiting this hearing to one group, ie Muslims. In practical terms, terrorism in this country simply cannot be understood in such a context.
There is a kind of terrorist sub-culture out there; gun runners, technical mercenaries like bomb-makers, criminal fund-raisers like drug dealers, scumbag lawyers, free-floating anarchists. These tend to operate in support of all subversives to one degree or another.
Beyond that, the unstable personalities who commit terrorist acts often adhere to views that the rest of us would consider contradictory. We saw this prominently with the Tucson shooter, but it is more common that not. For example, white supremacists despise American Muslims but many of them simultaneously express sympathy and solidarity with Muslim enemies overseas, ours and, especially, Israel’s. There is a lot of cross fertilization and overlap between terrorist groups, even when this seems irrational to the rest of us.
I really think that future terrorists develop their proclivity for violence first, then look around for a cause to serve as a rationalization. In Muslim countries, militant Islam is overwhelmingly the most obvious choice for this. In this country, there are many such choices but they all lead to the same place.