Why Home-grown Terrorists?

Home-grown terrorists aren't much of a surprise. This happens when people substitute their own self-interests with an ideology and abandon allegiance to a support system. We've had the American communists way back to the '30's through the '60's, some of whom spied for Russia. We've had the German-American Bund before WW2, and later the American Nazi Party. These are examples of groups who choose an ideology over their own national interests. Now we have terrorists of different stripes but mostly Islamic types. They reject police protection, fire protection, all the government support network that they get here, for a nebulous attraction to some terrorists who can't do anything for them.