Am I crazy for letting my 8 year old play Mortal Kombat X on PS4?

So a couple of days ago I was at my friend's house while my SO was at work. Her, me, her brother and parents were sitting down in the living room talking and I mentioned my 8 year old daughter (yes, DAUGHTER) on how she is so obsessed with Mortal Kombat that she never wants to go anywhere on the weekends. Then her parents called me crazy that I let her play that game and wouldn't shut up about it. I played that game so much ever since it came out that I really don't see a problem with it. Are my friend's parents right? Please comment 

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