It's not breed is it? It's training or experience
Yes and no.
Some breeds have been selectively bred for aggression, and for independence. They are often very powerful breeds, too, because they have been bred either to fight or to protect herds of stock fro wolves and bears.
A large, aggressive independent doglike this (eg caucasian ovcharka) needs careful handling and training - it's to to say they can't be good, safe family dogs, but they HAVE to be properly trained and kept under control, because they are big and strong enough to kill.
I know what @Peacocking means - sometimes you get a vibe of a particular dog, or breed, and you just aren't comfortable with it. I'm experienced and confident with dogs, and personally, I'd always trust my gut.
The only breed I'd put a blanket ban on myself (in the sense that I'd NEVER consider keeping one - not that I'd want to stop other people from having if they can cope with them) is an akita.
They are stunningly beautiful dogs, but the three I have known well have been aggressive and unreliable with people and other dogs. Maybe bad breeding - I don't know - but it's put me right off the breed.