Everything that leads to someone taking a violent action against another can be a lot of things. It can be something as small as how they were treated when they were young, mental illness, drugs, alcohol, movies, games, and even religion in cases. However, the one thing everyone has in common is the fact that most choose to do the things they see or hear about. Realistically people they the most they could probably do is force retailers to card people depending on the rating since. Take what our elected representatives as personal input to the situation for the time being.
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