Piltdown man, my friend, of course the pilot remaining in the cockpit has to fly, speak, and manage the aircraft. One would hope that the Captain would not choose the transit of the Atlantic weather convergence for the best time to head for the cawsey.
We are not asking the cabin crew to fly the aeroplane. Nor are we asking the latest youngster to join the crew to be the one to keep you company,just to open the door when the captain/first officer returns.
BUT as the female is almost never inspired to violent suicide...unless inspired by radical islam, just another person being there will make it more difficult to carry out your wicked intent. It has to be harder to kill one person who could be your friend, and is there with you, than to be alone with the autopilot.
Cabin crew, even the males, have to develop skills of working with difficult people; as opposed to some of the bad tempered scornful male pilots on this thread, including the one based in Quatar. The ones with long service have to deal with all kinds of drunken blokes inflated with self importance. Which would be more the type of persuasion needed than say karate training or using the fire axe.