Pitbull question...are they really that mean like they say they are?

I have a pitbull who is 8 months old and he is a huge dog but very nice and gentle big beast, we found him when he was only a few weeks old, we raised him to be really nice and til this day he is, he is very obedient and very very sweet. Yesterday I was having a conversation with the doctor that I work for and he noticed a picture of my family and my dog (the pitbull) was included in it and in the meanest way possible he said, " why would u have a pitbull those dogs are mean and r hardwired to kill anything" I was sooo mad that he said that n at the same time hurt my feelings cuz my Bruno is the sweetest thing ever he said to get rid of it before it kills my children, is it possible that he could one day bite or kill something or someone even though we have brought him to be reallly nice n obedient???? HELP PLEASE!!!!