I agree, the Dobies brain does not grow to large for its skull causing the dog to have a psychotic break and kill everything in sight. Nor is the old "they only kill their masters" saying true.
BUT, I think you are mad if you think these breeds are any less likely to behave inappropriately in the wrong hands. In the right hands, they are terrific breeds, like all other breeds. In the wrong hands, they can be as damaging as anything else.
I trust my Dobies, and one of them has actually bitten me quite badly. The fact I still have arms tells me he probably pulled his punches in a situation where he was terrified and redirected. That's a dog I trust because he has shown me his level of control. Far from perfect, sure, but there you have it, I trust him because I know him.
Leave him alone with kids or other people I don't know? No, never. Make assumptions that things will always be precisely as they are now? No, never. Assume my dog will never bite me? No, never.
But I do trust him to behave in predictable ways.