1. Reporting stolen bikes makes it harder to sell stolen bikes, making bike theft less profitable - and ultimately making it less likely that you'll be looking for a good deal on a new bike, since your old one won't have been stolen.
isn't (3.) 'knowingly' buying stolen property that is illegal? but 'unknowingly' buying stolen property would at worst mean you will have to surrender the property to the original owner?
2. Some people actually do care.
3. Buying stolen property is illegal