I anal, but I'm pretty sure that the law mostly operates off what the intent of a contract was.

You're begging the question here. He's trying to use spurious legal claims to prevent cancelling the transaction. His success at that can't make his legal claims valid.

At least in my country contract law is regulated by regular laws, especially contracts between consumers and corporations. There are definitely limits to what rights you can sign away and some of these are based on more general, open-for-interpretation definitions, using terms like "reasonable", "expectable" and the concept of "bonus pater familias" ("good family man", apparently referred to as the Man on the Clapham Omnibus in the UK), i.e., what would a regular, reasonable, moderately educated person expect. I don't know about America, but I would assume there are somewhat similar protections, at least for consumers.

Honestly, I'm almost in favour of letting the attacker keep the money to hold some of these foxhole converts to their own ideology. But I am quite sure that at least here, a contract which purports to be about proportionate sharing of a mutual pool of money but happens to contain a loophole that allows one person to run away with the pool would be void, and exploiting the flaw regarded in the same way as exploiting any other code flaw to obtain unauthorized access to a computer system - hacking.

Of course, my country's legal system has a often proven itself incapable of understanding how computers work, so who knows what they'd conclude, but I can't imagine that it is as clear cut as some suggest.