Re Paris not allowing you into terminals other than your flight's terminal, I propose a different way to look at it. The airport has chosen to simplify its own internal policies at your expense. If people can move around between different terminals, then they need to have policies about it, need to provide staff to check you as you move between terminals. This is easier/lazier for them.
I'm facing a similar annoying issue in HKG where, if on arrival you follow the signs for Transit in order to shower in a nice lounge, you CANNOT leave the airport afterwards and go into town. Why? Dunno.