You can provide access to information AND be kept from changing things that ought not be changed. I see no problem with this: VCDS, which is an aftermarket diagnostic tool for VAG (Volkswagon Automative Group), allows you to check lots of things, adjust some, and disallows modifications to others. I believe that owners should at least be able to know what the computer believes is problematic as this could point to something simple. And herein lies the problem with such tools- they give you something to go by but they're not going to tell you for certain what is wrong.
"Emission rules even make it illegal to replace some emission components with non OEM so once the OEM support is gone it’s illegal to repair. Stop the insanity as someone used to say."
Without seeing the specifics that's an overcharged assertion. If something meets OEM specs for the specified use/vehicle then it's legal. I don't see how any court could find otherwise.