Verizon has the right to transmit on spectrum allocated to it using consumer devices as its agents. It employs engineers and QA processes to make sure that any device transmitting on its spectrum plays well with others before it is allowed to leave RF-isolated testing facilities.
The public does not and should not have the right to transmit on Verizon's spectrum, even using devices they own which are legally and technically capable, except according to Verizon's carefully vetted programming. If they were able to run their own radio firmware, you'd have the situation described in the parent.
Cellular radios necessarily cannot be open source. The source could be released for inspection and audit, but it cannot be possible or permissible for you to run modified source on "your" radios.
Dude, that's exactly what he asked for.
Parent claimed that modifying the source wouldn't hurt anything since your phone can't transmit in ways you're not licensed to, but this is incorrect.
Nobody is asking for some sort of hacker radio anarchy, here. They're asking to see the source code for machines they own, machines that reside in their pockets, machines that are responsible for storing and communicating their most sensitive personal data.