Dog aggression has a genetic component. It's true there are some dogs that never display dog aggression. But to say that your dog is only dog aggressive because you didn't socialize it enough is false. There are some dogs you can socialize out the wazoo and they still will not like other dogs.
And, unfortunately, your dog will always be judged because of someone else's irresponsibility, simply because of the type of dog he is. It's a fact of life you have to acknowledge and come to terms with as an owner.