>Surely you can’t stipulate just anything in a contract and have that upheld as binding by a court, even in the US?
That's a great question. I'd expect that courts would not uphold claims to one's first-born child[0][1], but only because that sort of thing is already illegal (human trafficking). As for stuff that isn't illegal, I expect that YMMV.
That said, people actually "agreed" to give up/assign their first-born children with these "Click-wrap" agreements.
That people are so cavalier about such things should be a huge red flag for regulators to require not just a link to such terms, but that both parties should be required to demonstrate their specific understanding of terms and conditions before such a contract can be considered enforceable.
But that's not how US courts have interpreted this sort of thing. So, as always, Caveat Emptor!