Believe me, the cabin crew will have checked you all out from several angles.
I don't feel there is any serious risk. What you suggest would effectively be giving in to terrorism. We English will go about our daily business as usual.
More seriously though, the events of 9/11 have, I hope, crystalized everybodys' thoughts regarding what they'd do if confronted.
Would you remain seated and hope some-one else did the dirty work?
Incidentally, some years ago (90's) an unaccompanied deportee(low risk) made a run for the cockpit in a bid to get the aircraft to crash on approach into Dublin, I think it was.
He was stopped by the first officer (or hist fist) and was pulled back by two or three male passengers who saw immediately that all was not well!
He was sat on in the forward cargo while the captain completed the approach and landing.