The alternative of course - according to you - would be to allow them to get as close as they want.
And...if it turns out their intention is really bad and let us remeber this is a nuclear WARSHIP and they get on board and manage to do "the impossible" ....what would you say then???
Oooppssss????
It would be I suppose the fault of the Yanks who brought the ship here and not the dead-sh#t lunatics who did their worst??
Maybe shooting them at 50 meters is draconian but if they attempt to board - shoot to kill!