I believe that no Cellular Telecommunications Company (Cell Carrier) has the right to lock a device to allow only their approved software image on a device fully owned by the consumer.
When a cell phone is purchased it becomes the property of the purchaser. To allow a Cell Carrier to continue to dictate the types of software that can be allowed on a consumer owned device removes the consumers right to personal property.
Further, by restricting the administrative access (Root) and locking the software (bootloader), the Cell Carrier is preventing the consumer from using the device to the full extent and it remains under the control of the Carrier.
Any Cell Carriers claims of security vulnerabilities are null because other "Unlocked" or "Google Edition" devices are allowed on the network