Dogs bite, dogs bark. They're an animal and animals can be unpredictable. Is a pitbull much stronger than a chihuahua or retriever? Yes. Is it inherently more aggressive? No. A pit has the same likelyhood of biting you as any other dog breed. They're just more dangerous when they do wild out because they're a breed who've been bred to do as much damage as possible.
The dog itself isnt the problem because any dog can bite. The issue is the owners who dont have the patience to raise the dog to do well around others, or who get the dog because they're insecure and want to appear tougher than they actually are.