And then imagine how dangerous it would be if someone could just fix their HVAC unit on their own! Or their own solar charge controller! What would the world come to next?!
Since you brought up refrigerant I'll go ahead and point out almost anyone can buy propane anywhere, including kids. It's a great refrigerant, it just can't have any trademark or patent protection.
To compare this to the DRM placed on tech products, I'd need to have a cryptographically signed refrigerant bottle to recharge my AC.