Since when did American astronauts land anywhere?

I remember the space program very well. Not one of the astronauts "landed" because that would have killed them. They *splashed down* in water, surrounded by an entire American naval fleet.

Now can you explain any plausible scenario where a handgun would be useful?

Suppose for example that in the moon landing, the Russians had driven away the huge aircraft carrier USS Hornet with destroyers. Then the astronauts get out, with a handgun and... commit suicide? Shoot a couple of Russians and get confined anyway? Use their pistols to take over the Russian destroyer?

I would say that your determination to that the astronauts must have a gun without any scenario where it would possibly be useful proves my point very well.