They can make killing multiple people in specific locations more difficult, but they do nothing to keep someone from being able to fire a single bullet for an immoral reaspn, hence the difference between lethality and identification and morality.
The Vegas shooting would not have been less immoral if a single person or nobody died. There is a benefit to reduced lethality, especially against crowds. But again, reduced lethality doesn’t reduce the chance of being used immorally.