Because in some devices, to restrict the baseband from interfering, you also have to lock down the OS to the point where the user can’t modify it.

I don't think "My decisions have made it hard for me to comply with this reasonable regulation so I shouldn't have to" is a very good argument.

People should be punished for doing illegal stuff, not for being able to do illegal stuff.

There is not much constructive use for something that would breach these regulations. Contrary to some of the FUD being posted in this thread, the regulations don't appear to be about custom firmware for the UIs or even signalling on a device. They're about the control software for the radio itself, to ensure it plays nicely with everyone else. That software is typically extensively tested and certified before being licensed for use, and any supplier whose software didn't work properly in the field could expect a very rapid and unsympathetic response from the authorities.

What a lot of people fail to understand is how disruptive a radio device that doesn't follow the standards can be. I worked for a radio network operator for a while. One day I got into work to find there were widespread reports of radios not operating properly across a major city. Someone was transmitting something out of spec and causing sufficient interference to effectively bring down the whole network. Do you know what happens at that point?

This is what happened that day. Real people got into real vehicles and started moving around a search pattern with relatively crude sensors, trying to locate the source of the interference. And then when they found it, they had to figure out how to shut it off. That involved gaining access to premises where the rogue device was located. Ideally you do that with the consent of the residents, because the operator of the rogue device may not even realise that it's not behaving correctly. Worst case, you're looking at forcing entry, which means bringing in other public services who are allowed to do that sort of thing with the appropriate authorisations, which in turn have to be sought from the appropriate authorities before anyone can move. And then once you've got into the premises you still have to find the device itself, and then you have to figure out how to turn it off.

Contrary to any movies you've seen, this process can take a considerable time, probably at least several hours unless you're very lucky. During that time the entire system will be operating at reduced capacity, if at all. Think about the range of a modern cell phone, and consider that any device that can transmit over that range can also interfere with the control channel for any signalling system within its range. Also consider that we're talking about changes that might increase the power and therefore the range of the device, or might change the device so it's using different frequencies and disrupting other forms of transmission/communication, not just whatever it was designed to work with originally.

Bottom line: even one small rogue device on a radio network can cause serious disruption over a wide area, and not all devices covered by these regulations will be small or have relatively low-powered transmitters. Imagine a whole city block or business park where wireless devices didn't work all day. Imagine a whole city where mobile/cell phones weren't reliable. Imagine a major incident where emergency services couldn't communicate properly to co-ordinate their response because their radios didn't work, or where the entire response was delayed by several minutes because no-one could find a landline to even call the emergency services in the first place. You get the idea. And just to be clear, this is not some paranoid fear of a hypothetical problem. It actually happens, just fortunately not very often, thanks in large part to the kind of regulatory regime we're talking about here.

It's true that with any sort of government regulation you have limitations on individual freedom. Laws do that, and should never be made lightly. But at the risk of ending on an inflammatory note, consider that while people can hold strong views on whether private individuals should be allowed by law to own and shoot guns, and reasonable people can debate the pros and cons of that, no reasonable person thinks it's a good idea for anyone who wants one to be allowed a WMD where they can push a button and kill everyone in a city. There simply aren't any good uses for that kind of technology, and the damage one person can cause to others is wildly disproportionate to any personal freedom given up by someone who for some reason wants such a device even though they can never use it. Obviously I'm not suggesting the threat from a rogue radio transmitter is comparable to the threat from a nuclear bomb, but it really is a significant risk and even potentially a matter of life and death.