People made the same argument in Canada but they changed the rules so you either get an unlocked phone or they have to unlock it upon request. Yet there has not been widespread issues of this happening. They can still ding your credit & there is only a small number of carriers so you can only do that so many times before you are going to have serious issues if you don't care about your credit or collections.

Also you can still get the phone unlocked without the carrier anyways if you really want to so it would not deter anyone who really wants to run off with the phone anyways.