T-Mobile, AT&T oppose unlocking rule, claim locked phones are good for users

This is a good way for Ars to generate clicks and a more honest headline probably wouldn't move the needle much, but it's worth being clear for HN that the objection here is not that locked phones are good for consumers, but that the subsidization deals locked phones enable are.

Why do you need to lock the phones for this? If the point is to lock customer to a subsidizing contract just do that: use the contract to enforce the lockin. What do they care if I use another sim card on the phone if I'm paying the monthly service for the duration of the contract?