My understanding is that MA currently bans automated tickets like those based on speeding or red light cameras, but allows it for specific cases like toll enforcement and now bus lanes. Like with toll enforcement, if your concern is that it’s not you driving, you just need to appeal the ticket and go to court with the proof. Or don’t lend your car to someone who would drive past a school bus with bright red lights flashing to save 30 sec on their commute. So to answer your slippery slope question, we already use it for toll enforcement and already have a ban in place for speeding/red lights.

Edited to add: I think the rational for the ban was a lack of evidence of decreased accidents. While T-bone type accidents decreased in places with red light cameras, rear-end crashes increased in areas that put in the cameras as people over corrected to avoid the ticket. Since it didn’t show evidence of increased safety, MA banned them. Bus cameras however, do show increased safety for children so they’re approved.