If that was true, I would have to agree to YouTube's TOS to watch videos. That's not required, so there's no legally binding agreement between me and YouTube since I haven't actually signed or accepted anything. My understanding is, I'm not bound to something that's hidden in a link somewhere and never presented to me.

But even if I were legally bound to the TOS, nothing in the TOS says copyright is granted on the condition that I watch ads. This is the closest that I could see:

The following restrictions apply to your use of the Service. You are not allowed to:

...

2. circumvent, disable, fraudulently engage with, or otherwise interfere with any part of the Service (or attempt to do any of these things), including security-related features or features that (a) prevent or restrict the copying or other use of Content or (b) limit the use of the Service or Content;

I don't think blocking ads counts as "disable... any part of the Service," it's just blocking certain web requests. It's close I guess, but it seems they're more worried about "hacks" on the service to get access to things you're not supposed to. For example, accessing adult content w/o making an account would probably count as a violation under this TOS.