I don't need to agree to any terms to be able to make web requests and receive responses. That's just a normal, legal thing to do on the internet.

The GPL is valid because it grants you license to do something that would otherwise be illegal i.e. make copies of a copyrighted work.

I have access to whatever site by virtue of the site responding to my requests. In the absence of the ToS I can do whatever I want and the ToS serve to restrict that. In the absence of the GPL I can do a strict subset of what I can do when the GPL is applied.

My interpretation would be that software licenses like the GPL can really only be violated by people and companies that have the capacity to understand them. Asking a layperson to sift though some sites ToS is a burdensome expectation.