The point is not to stop your ISP from showing you ads. The point is to stop your ISP from interfering with your traffic in transit.
If I ran a website with ads, and someone was stripping those ads to replace with their own ads, I'd be annoyed. I'd be amazed if that's something Google would tolerate. We've seen plenty of stories from people saying "Google closed my ad account and froze all my money!!!" so I hope they do that to this ISP and or the company serving the ads.
But you already don't stop your ISP from interfering with your traffic in transit. So why is it a big deal if you continue to not do it? Or is seeing a few ads more important to you than, say, all of your email?
For what it's worth I was grumpy in those situations too. I wrote polite letters. Where possible I opted out.
But your point - this kind of this happens all the time, and has been going on for years, and noone is doing anything to stop it even though it's wrong - is taken.
If I ran a website with ads, and someone was stripping those ads to replace with their own ads, I'd be annoyed. I'd be amazed if that's something Google would tolerate. We've seen plenty of stories from people saying "Google closed my ad account and froze all my money!!!" so I hope they do that to this ISP and or the company serving the ads.