So let's assume that the government decides to place an armed policeman on your flight one day. He will somehow have to circumvent all the security without giving himself away to the hundreds of people who see him in the terminal. Or perhaps he will pull up at the aircraft side in an unmarked police car and run up the steps.
But surely he will have to declare himself to the crew? Imagine the scene if a cabin crew member caught a glimpse of his gun in its holster? Wouldn't his identity have to be made known to the flight crew? How will we feel knowing that there is a loaded gun on board?
He cannot therefore remain anonymous. The young girls will be chatting him up. He will be unduly familiar with the entire process and environment on board. Soon he will be bored and perhaps lose alertness, regardless of his professionalism. I like flying, but a long flight renders me zombie-like.
With all this in mind, I find it hard to imagine being prepared to operate a flight under these circumstances. I will step off the aeroplane, and tell the company to find someone else. I suspect I will not be alone.