I dissagree a little bit in that you NEVER leave a baby with anybody else. There are people you trust and that is OK. I left my baby with my father while I was shopping and I was reassure nothing would happen to him. Or you can have very close friends. I know people with kids sometimes cover up for each other. There is nothing wrong with it.
I do agree with you. I can trust even my dog, but only after months of watching and judging how they act and feel about babies & those who are weak and need protection. (She actually bit my father-in-law who was 'sneaking' up on the baby while trying to play)
I just like the default setting of NEVER for safety. Of course you can relax that once your better judgment tells you it's ok - friends/relatives whom you trust with the life of your child. What's at stake is so precious, that when there's even the slightest sliver of doubt, I'm not leaving the baby with anyone/thing.