I know it's not unique to America, but I think we have a particularly strong issue with a sort of fatalistic fantasy role play. Our culture places a lot of value on justifiably killing people. The old trope of the every day "good guy" taking the law into their own hands is bedrock deep. We practically worship it. Laws like this give weak, cowardly, pathetic dudes the final push they need to not just kill, which happens all the time, but to be in a position where they think they can be praised for killing someone.