The way this was explained to me, and a phrase that I think is very powerful, is that for a contract to be valid there must be a "Meeting of the minds"
(IIRC there must also be two parties (otherwise it is a deed not a contract) and the parties must have "capacity" i.e. the potential to fulfill their obligations)
IANAL - probably painfully obvious to anyone who is.
Law is like code (and magic) - it is a framework that gives real world power to abstract language - maybe this is why HN is so obsessed with legal chitchat
Which is somewhat absurd, since most people agree to hundreds of ToS contracts without reading them.
And the legality of this isn't fully established; in fact, last I heard, it was being somewhat successfully contested. But there's no sweeping word on the matter yet: you could probably take a ToS violation to court and have it set precedence.
Be careful not to confuse criminal law with contracts. It is fundamental to the existence of a contract that both sides understand it. That is one of the few points of law that is pretty much a universal constant, whatever jurisdiction you're in.