I did TKD from when I was 7 until I was 12. I received my black belt when I was 12 and competed in several national championships. TKD was a great martial art for me as it allowed me to learn the art and skills, but really instilled some great values in me that contribute to who I am today. I have never been in a fight aside from in competition and I am actually pretty proud of that.
So, I would suggest finding a gym that seems respectful. Find a place where your son can go and learn the art and also continue to build strong personal values without even knowing it.