Earlier quoted context omitted.
> I wonder if you can click on "I agree", and lie. Then you wouldn't be bound by the terms, because you didn't consent to them .... It doesn't work that way --- courts look to objective manifestations of consent, not subjective intentions. In kids' terms: Crossing your fingers behind your back doesn't get you off the hook.
There is however a reasonable chance the person clicking I agree is not the end user. Setup a Facebook account for your grandparents who never click agree. Are they then bound by the TOS? In the end TOS are generally weakly enforceable. If facebook adds a 10,000$ annual fee in the fine print and there unlikely to be able to collect.
My guess is that a court would ask: Can you reasonably be said to be the "agent" [1] for your grandparents --- that is, would a reasonable person, taking an objective look at the facts, conclude that your grandparents had authorized you to make binding agreements on their behalf --- for the kinds of transactions specified in the TOS?
If that's the question, then:
-- You probably are your grandparents' agent when it comes to agreeing, on their behalf, to the "customary" terms in TOS, such as (for example) a statement that the Web site owner owns all content;
-- You probably are not your grandparents' agent for purposes of agreeing to pay a $10K annual fee, and therefore they wouldn't be bound. (You might be bound, though ....)