What a dumb, emotionally-driven slit.
It would have meant that the plane would hit its intended target - just as it did.
However, an armed crew member would have increased the chance that they would have never gotten control of the cockpit. No downside - only an upside.
Other than the obvious answer, YES, the other answer is "Why, no, I'd much rather THE gun in the cockpit be in the hands of THE terrorist!"
It doesn't even LOOK right when you type it! I can't imagine what I'm not "getting."