I don't trust them. Large dogs could fuck you up if they decided to. People have a wierd attitude about their own dogs too. Its always "he's just a big sweetheart, he'd never hurt anyone...". They're all absolutely honestly bumfuzzled when it turns out that, under some circumstances, fido is perfectly willing to hurt someone. In practically every dog attack, the owners never see it coming. They never see any signs of any impending danger in the behavior of the dog.
Think about that, large dog owners. Right now you're reading this post thinking " this obviously doesn't apply to my sweet big ol teddy bear of a dog, aww he's so cute *snorgle*". I'm telling you that the very same wool that was pulled over the eyes of countless loving dog owners whose dogs ended up hurting someone is currently obscuring your vision. Perhaps it obscures all our vision. Maybe you just can't tell. No matter how sweet and loving and wonderful your dog is, he might snap one day, and you might not be any smarter than the other people who didn't see it coming. Just think about it.
Edit: Also, I have a cat. If one day, my destruction becomes her sole purpose in life, I'll just stomp her to death or something. My motto is don't own an animal you can't stomp to death in a pinch.