It is completely understandable for someone who had a negative encounter as a young child with an aggressive animal to dislike/distrust that species. It's also likely to be a continuously reinforced dislike, since dogs especially will respond negatively to fear and distrust. They don't know why you're afraid of them, and assume the worst....because that's what their pack instincts tell them to do.
My dog is both a joy and a pain in the ass. It's a double edged sword having a highly intelligent dog. They're more than capable of training YOU, and you need to guard against it. My girl is extremely sensitive to body language and smell, especially the family's. She picks up on vigilance on my part instantly, that I know no human has picked up on. She's especially sensitive to, and protective of, my wife and daughter. If they are quiet apprehensive, the dog will definitely keep an eye on a stranger, and let the stranger know they're being watched. This is not a foolproof system, though. The dog is also distrustful and occasionally nervous around disabled people, who's body language and affect can be 'off'. So there can be 'false alarms' so to speak. But she's definitely part of the family, and makes me more comfortable being out of the house. I dont want to be without what a dog brings to our family.