Yeah, agreed. I'd sooner just get used to carrying a helmet around with me than share one. Sharing one with people you know is bad enough, but not with the general public. That said, you can mitigate that by what you wear between your head and the helmet.

A hood or legionaries cap would provide some separation, however not everyone appreciates the extra insulation around their heads (which radiates most body heat) and having anything hard protruding out from underneath the helmet (such as the peak of a cap) is a really bad idea since it's the first thing that will hit the ground if you come off.

Melbourne seems to have got the better deal in this regard, you pay the money and the helmet is yours. The downside is the cost of subsidising and administering the scheme.