Trouble is, we still don't KNOW whether the hijacker is intent on wrecking the craft. The hijackers in Sept 11 lied and promised to land the craft safely.
From now on, we must assume that every hijacker is a suicide bomber. Should we or the authorities err in some case, the onus is on the hijacker. The suicide bombers have forever changed the rules of engagement.
The point is, that we don't just want to answer a hijacker by having some citizen cowboy pick up his land-trained six-shooter and drill holes in both the hijacker and the plane.