1: Ad companies are not going to go after individual users, rather they would target the maker of any such plugin
2: If they did go after an individual user, they would have to prove damages, and an individual is unlikely to do more than a few bucks of wasted ad spend for a company, not even a rounding error, making the legal cost and political cost of targeting the person running the script enormous compared to the potential return from anything other than a grand slam nuclear judgement in their favor.
2) Yep! And as mentioned in other threads, it would give the users on their ad platform more money but degrade the quality of their ad platform.
I was just alarmed by how many people are not only okay with, but defending, the current state of ad tech. I think it's a noble effort to go against the grain and withstand any potential legal trouble to subvert it as it seems there's no recourse to be made in the courts unless an entity has the aforementioned time and money to fight it in the courts.