Thing is, apart from a shotgun, which I believe can be used without a licence, at least by a farmer, to kill vermin, anything other than an air rifle would likely need a licence, so borrowing/lending one might leave him/owner the gun on the wrong side of the law.
In the wrong hands, anything from a baseball bat or catapult can be misused, so not confined to air rifles. My sister (before retiring) was head of a primary school. One summer, when there was some playgroup using the ground (school buildings locked) some yob started firing his air rifle at the school.
Smashed several windows, and where he was firing from, pellets had to be fired above the children and adults with them.
Took 4 hours for the police to turn up (my sister drove there as soon as caretaker rang her to explain situation), so no chance of them taking action or catching someone "in the act".
In the meantime, my sister had printed up notices about the disgraceful activity of someone on the estate and hand delivered (she knew exactly which house, but not the individual lad)... probably some parents sorted it out, one way or another, when they knew what had been going on!
Took at least 2 days to carefully clear up inside the school, with glass splinters in books, shelves, etc, etc. All caused by some stupid idiot.
But while some might argue against air rifles, others could argue against cars being capable of high speeds, given the numbers of deaths on the roads every year.
Banning them doesn't rid society of them - too many in circulation already.