Bear in mind that not every dog that "charges" intends you harm.
You probably greased someone's pet.
Great, you have a deadly weapon. You just haven't had a chance to actually think before you use it. Remember this about dogs.. they often have a reason for doing what they do.
I had a large retriever walk up on me one night when I was walking down the middle of the road. When I stopped walking forward, the dog stopped moving toward me. He was silently protecting a twenty-something who was unloaded a car in a driveway on the opposite side. She saw me and called him back. Sure, I was dead to rights to kill the dog. But he wasn't snarling, barking, or anything like that. And she called him back.
At the end of the day, I went home without any holes in my soul or self, she did the same, and the dog did as well.
I've got a friend who owns a pitbull. And he's the nicest dog you'll ever meet, but he plays like a bull in a china shop. He's big, friendly, and all over the place. Hasn't hurt anyone and I don't expect him to. But like you, I had my reservations about the dog from the breed. Experience has shown me that he's no less tenacious than a miniature schnauzer. He just has the mass to back up his actions.
I worry less from a dog than a human. Dogs generally "tell" when they are about to strike, or for some reason that's usually visible. Humans are more subtle.