> you can just regulate against it, problem solved

I think that is exactly what you'll lose the ability to do. If Marvin Heemeyer didn't need the town's septic connection we wouldn't know his name.

A huge fraction of regulatory enforcement exists in the gray area of "the government is wrong, or their enforcement of it is wrong but it's cheaper to bend over and take it than to fight it through a courtroom". If farmer Johnson can slap up a building kit on his property and power it with stuff he bought online and doesn't need the power company, Joe Schmo can do the same with an ADU. Yeah, they'll both get dragged through court but $50-100k of court costs to be proven right is a much smaller threat when the project can be done and generating income for the duration of the court case (it also renders the typical tactic of dragging out such cases much less effective).

And at a slightly larger scale, if some business interest can negotiate purely with a municipality to take over some disused factory and bring it back into use and get their power via bunch of panels and not get bogged down with state permitting to get a transmission line and substation the state loses a huge number of levers over the business interest and also they lose levers to control poorer municipalities (who'd happily take the business). Once again, they'll get dragged through court by the state, but spending 5yr and $200k just to be right isn't a dealbreaker when your widget factory has been operating the whole time.

Yes, of course governments can do worse things if they feel like it, but they run into problems of political optics and will more or less instantly.

You already see this kind of thing in some of the highest cost areas. Certain demographics in the greater NYC area often do building and land development things this way. It costs the same at the end, but by doing it without asking you get to use it while the whole process runs.