If the bike theft rings don’t want them, I was thinking that the people who rent them just won’t bother to bring them back. They will end up being the equivalent of urban shopping carts.
Unlikely. I've looked into joining this thing because there are a few bike stations within a block or two of my job, and the pricing structure really discourages theft. The first 45 minutes are free, then a couple of dollars for another half hour, after which the fees begin to mount up very quickly. After 24 hours, a bike is considered lost/stolen, and the renter is charged $1,000. Pretty strong incentive to return the thing.
Obviously, fake credit cards could lead to this kind of theft, but again, sophisticated credit card theft rings have better things to do with their stolen card numbers than to steal a big, ugly bike that they would have a hard time fencing.