I agree that you cannot trust all animals. I work for a vet and let me tell you there are a lot of animals you don't want to be sticking your fingers near. I've been bitten by a pug, lunged at by a rottie (luckily the owner had her leash on-or I'd be in the hospital), scratched I don't know how many times by cats, etc....
I trust my own cats, I trust my friends cats but you always have to be wary of strangers animals or you could wind up getting hurt. Now that doesn't mean that you have to scared of everyone's animals, you just have to be careful.