Advice or kind words about owning a dog, please?

Some background info first; I own a bull mastiff/great dane. He is ten months old and about 90 lbs and he is very well trained. I live in a decent sized three bedroom duplex that my fiancee and I bought. He works afternoons, 2 to 10, I work part time as a deck hand on a dog friendly boat, so Logan (my dog) is rarely alone. But I have been put down many times by people telling my that I am an irresponsible dog owner because Logan is a rescue from a dog fighting ring and is very scarred up. Ive been told he needs to be put down, he is going to kill someone, etc. All by strangers. He loves babies, is scared of cats (and spiders) and is very gentle when he plays with my moms chihuahuas, all under 10 lbs. I guess I just want advice on what to do when people say that. How do I deal with people telling me that they know my dog better then I do?