I'm not a lawyer, but I tend to think that it would not be a clear-cut argument. On the one hand, it is a TOS, which is a contract. On the other, people don't read TOSes online, and I have no idea what the current case law has to say about that. Even if they did read it, it could be argued that a "signup for free" button that is generally available, without an approval cycle behind it is an implicit written permission for anyone to access the services.

Again, IANAL, but I certainly would not make any decisions on the validity of this without consulting one.

Why wouldn't it be? They say you have to agree to it to get access, so the copiers that made accounts agreed to it.

If you mean, "would be defended" or "could know about it", then probably not. It just adds more to the name and shame tactic they decided to do.

Here in Belgium, there are terms that people put in their legal document that shouldn't be present and would be considered invalid (as if they were not present) irrespective of the fact you agreed to them.

Examples that come to mind: prohibit people renting an apartment to have a cat, reduce the time you have to return a product bought online (and get a refund) to less than the legal time, ...