I love dogs. That said, yes, they can scare me. I've seen large aggressive dogs that are not properly trained and it makes me uncomfortable. It's not the dogs fault obviously.
I‘m less scared than just not a fan of the idea, they’re usually very slow and, I‘m afraid, much more unreliable. Technology like that should be tested more before giving it out into the public. I‘m not sure whether there are any known cases of crashes or accidents, but considering you are letting a computer drive on the streets with other REAL people, who also make mistakes often, the chances are higher the computer can’t detect their behavior correctly.