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.
But, now they've seen their ISP tampering those people might switch on encryption for their email, and everything else.