It would be less unacceptable than killing 58. Neither, of course, is acceptable - but the fewer murder victims, the better.So if you had a revolver, you could kill half a dozen. Would that somehow be more acceptable?
Also if you had a revolver you wouldn't be able to kill six people in a crowd unless you nailed them to a wall first. To kill those 58 people, the Las Vegas shooter had to fire 1100. That means he had to fire 19 times to kill one person, on average. Assuming the revolver owner was as accurate, he wouldn't kill anyone with his six rounds.
And THAT is definitely more acceptable.