you can make an explosive by mixing some liquids brought on in your toiletry kit, disguised as harmless bottles of shampoo or cologne. is that "obviously dangerous"? if I see some ME guy doing that, should I be concerned? should someone try to stop him? Is mixing some liquids from your travel kit a typical thing that a passenger on a plane does?
All good questions, and there are no easy answers. I suppose you have to decide if you want to risk being hauled off to jail and being convicted for assaulting someone on a plane for no good reason, or if you may be stopping a devastating terrorist attack.
And I'll ask you (as I just asked someone else), how do you tell the difference between "some ME guy" and some Hindu from India?
It's a judgment call and, like I said, one with no easy answers. My only solution is that I won't fly any airline other than El-Al, until the others stop with the politically correct horse crap and start aggressively profiling and investigating each passenger before they ever board the planes.