I agree with you fully on this. Unfortunately, the odds are stacked very unfavorably against us. It's not just the manufacturers who resort to these underhanded profiteering tactics. Even the regulatory agencies are for locking down the firmware.

Their argument is that an unlocked firmware would allow us to override regulatory restrictions like the RF output power or the IMEI number. That argument has some merit. However, my opinion is that such restrictions should be implemented as hardware interlocks that are unchangeable through software. Thus, we would be free to change the software as we like. Sadly, both the manufacturers and the regulatory agencies tend to completely ignore that solution, so that they can retain their excess control.

It's trivially easy to break those restrictions with off the shelf SDR hardware you can buy rather cheaply.

Locking people out of their phone does not raise the skill or effort ceiling much, as there still presumably would be software restrictions in place.

I always found this claim completely bogus, you can always do something illegal with your phone, there's no way to prevent everything with software.

This is the goal of law enforcement and justice in general and in this argument, a hardware manufacturer is substituting this role, when we say that, we can see the overreach. Manufacturers aren't public entities able to make such decisions.