Why are people such cowards?

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This weekend, my cousin was at a party, and he got into an argument with some guy, and they ended up in a scuffle. Not a good situation, but fair enough, right? Until the other guy's buddies pulled my cousin off and held him down, and the dude proceeded to beat him with a stick. It turns my stomach. I hate violence, and I just wonder how people can be so cruel and such complete cowards. Any thoughts?