I didn't say that it was the biggest threat right now. I said that that we don't need additional violence (on top of our own domestic urban gang warfare, etc), and that long-term, if we don't get smarter, Islamic fanaticism/terrorism would become the biggest threat. By saying "if we don't get smarter", I'm referring to irresponsible decisions by some nations to allow large numbers of immigrants/refugees/economic migrants from muslim majority countries.
Etiology is very relevant here because we can reduce further Islamic fanaticism by just not allowing muslims in our country (or my preference, to decrease the numbers, and ensure these people are vetted really well). On the other hand, I'm not sure what we can do to stop gang violence, and the reason for that is that its cause(s) are different. So, I don't see how it's relevant to compare how many people die from gang violence to Islamic terrorism. And I don't see how it's logical to say because x causes more deaths right now, y is being over-blown.