Mass surveillance may be illegal anyway as you say, but what is the relevance of that? I hope you don't take it being illegal to imply that the government isn't going to do it.
If you think the gov't is doing illegal things to US citizens then provide the proof and expose it. I don't have evidence so I am not going to speculate either way.
Doesn’t matter whether usage is legal companies are allowed to enter into contracts as they see fit. That’s a core principle of a society with free speech. If Anthropic said you weren’t allowed to use Claude on the toilet they are writing the contract.