Would I do it? No. Even if you could see the door; what if there was an emergency in the room? The only time I have ever left my children "alone" was to sit directly outside the door while they were sleeping to have a glass of wine with my DH. Would you leave them alone at home to go to the neighbors house where you could still see your front door?
I'm not the OP but I would have no problems with leaving a sleeping baby or children to go to a neighbors house. Why would this be a problem? By neighbor I'm assuming someone within sight and walking distance of your own home, not a friend across town. When I was a baby my parents left me sleeping in my crib to get together with all the other neighbors in their court.
I wonder how far things will end up going. First we're afraid to go a house or two away from our babies because think of Madeline McCann, anything can happen. Well what about we should never leave our pre-teens asleep in their own bedrooms, think of Polly Klass or Elisabeth Smart. 20 years from now will there be post about negligent parents who went into their own kitchen without lugging their 6 year old with them, or a mom who threw on a load of laundry in the basement while leaving her 10 year old all alone in the living room, where of course anything could happen. 30 years ago there wouldn't of even been a question, every parent would be out in the pool after getting the little ones to sleep, I really fear where we will be 30 years from now.