It's a matter of culture perhaps.
We lived in France where parents would take their eldest to school leaving the babies at home in cots. When we asked neighbours over the square to babysit they turned up, set the baby alarm up and went back over to their house!
It's all a question of risk too.
For me the stats on babysitters who have abused their position are much higher than the stats on children who have been abducted. If your child is going to be abducted or abused then this is much more likely to be perpetrated by someone you know. Stranger kidnappings are so rare that people can still only think of Madeleine McCann who was taken from Portugal almost 10 years ago.
Fire risk - yes there is one but if a house is fitted with smoke alarms and everything is turned off then you have minimised that risk. To my mind, being 10 doors down is no different to being at the bottom of the garden. A smoke alarm would alert you to a fire way before you saw any smoke.
A good baby alarm doesn't just pick up sound, you can now get ones with video monitors and which record breathing. That also lessens the risk.
I would far rather have a video baby monitor on my child than hire a babysitter who I might not know.
But then I might consider other things to be a risk that other parents would happily do, like letting primary school kids have a sleepover with friends. I wait until secondary school before I start sleepovers. I wouldn't threaten those who have a different perception than me with social services though on the basis that their friends' parents might be child abductors.