Agreed. A carrier should never be allowed to brick your phone.
However, they should be required to participate in blacklisting phones reported as missing or stolen. At a minimum, it should be a national registry. Preferably, it should be international.
I have seen a number of Verizon branded phones on Craigslist that have been supposedly reflashed for use with Cricket. I wonder how many of those phones have unclean serials. Same goes for AT&T branded phones for use with Rogers.
Second, if a stolen phone attaches to the cellular network, the carrier should be required to contact the police with location information. If a missing phone does the same, the carrier should be required to contact the owner (charge a finder fee if lost, contact the police if stolen).