Although I don't have children I know that when I do I wouldn't go for a drink and check on my kids every half an hour, I'm far too negative a person and I always think the worst will happen. However, that's not to say I wouldn't make some other 'mistake' that would lead to something happening, such as letting my child walk to school or to a friends house.
There is no right answer and the people debating will just continue to go round in circles. I was talking to my mum earlier about this. Both her and my dad have been the greatest parents imaginable to me and are both very intelligent, but had a raging row when I was younger about whether it was acceptable to leave me and my sister in our room at Butlins while they went for a drink. It was simply the done thing but my Mum wouldn't allow it. Different people judge situations differently, it doesn't make them bad people, and as has been said numerous times, I'm sure they are suffering enough.