That's certainly possible, but unfortunately, I think they're still in the coalescing phase, where their differences matter less to them than their common desire to destroy the US.
Many old-line terrorist groups, for example, are forming new alliances with Islamic militants. The head of the Basque terrorist group ETA in Mexico (long one of the fund-raising headquarters for ETA) converted to Islam a while back, for example, and Islamic "missionaries" are busy among the more traditional left-wing Mexican Indian groups in Chiapas.
I think you're right about the author's problematic response. Much of it(emphasis on "American right wing" groups and "root causes") seems to reflect Clinton-era thinking.
I am curious, how did this epiphany go down with his troops?