The ad blockers this affects are popular because they do more than declarative black lists. It may make them safe by design, but it also makes them something completely different and less capable than what they are today. There's some room to be suspicious about that.
That's totally fair. Nobody except the people who proposed / approved the project know what the main motive was. It could be trying to hinder adblocking, could be security, it could be performance, or it could be that somebody just wanted to copy Apple.
If we as outsiders try to reason about that decision, it makes sense to pick the strongest version of those motives, not just strawmen. There's a good security argument to be made, and a silly security argument. If you pick the latter one to argue against, of course it will look like a bad excuse, leaving the more venal explanations as the only possibilities.
