Honestly these threads make me laugh.
The reasons why you shouldn't, I mean.
"You might get hit by a car" (in which case, being alone in a cot for a few hours is the least of its worries, growing up without a mother!)
And if you were hit by a car but had the baby with you, that would technically be worse for the baby, non, because he would also be engulfed by this previously invisable silent car that nobody could see coming 
Fire breaking out - well, its across the road so not a massive difference in terms of response than if you are putting the bin out, really!
If it were me and I really needed something (like wine) and there was a shop literally diagnoally opposite and my immobile baby was asleep and down for the night, well, I reckon I probably would. This is a hypothetical scenario though, as I don't have a shop diagonally across the road.
It looks bad on paper, but in reality, the likelihood of it going wrong is actually probably statistically much much less than if you took the baby with you or if you just went out in the car the next day or whatever. But hey. Its not advisable, shall we say?