System wide ad blockers can’t block a lot of ads, namely same-domain ads or those that are built into the html. Much rarer than the external page kind (DNS ones) thankfully.

It’s not stealing, it’s unauthorised redistribution. They don’t lose anything from piracy, except for potential customers, which is a pretty intangiable concept. Don’t think it’s even remotely as bad as going into a tech store and taking all their DVR’s, or even literal piracy by chasing down another boat with guns and taking their cargo.