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How is it ironic?

the fact that a law is enacted to protect people from "killing each other" and that this is unnecessary because weapons are only a tool for self-defense. demonstrating the collective stupidity of the government in creating unnecessary laws.

I wouldn't rest any argument on the assumption that weapons are only a tool for self-defense. No one would ever be able to prove that assumption, and thousands of years of human aggression would seem to disprove it pretty handily.