This is something that tons of people have written about---I'm not a contracts expert, so I don't want to opine too directly, but I will say that lots and lots

This is something that tons of people have written about---I'm not a contracts expert, so I don't want to opine too directly, but I will say that lots and lots and lots of people have criticized the idea that hidden contracts will be enforced. Some courts have enforced them, some courts have refused to enforce them, and the law is a little bit tangled and complex (hence why I won't speak to it with confidence). Those people who defend the enforcement of such contracts basically think that (a) consumers generally know that there is some contract, and can always ask to see the details before they buy, or demand a refund if they see them and they're unacceptable, (b) there will probably be some broad based public policy or unconscionability constraints on contracts entered into like this---nobody in their right mind, for example, would enforce a software contract that says that when you install it you promise to turn over the entire contents of your bank account to Mark Zuckerberg, and (c) it would be blindingly difficult to disclose full complex contracts before every consumer transaction anyway. As you can probably tell, however, I'm with the critics---I think such contracts are fundamentally bullshit. It has always seemed to me that the right answer is to enact a set of fair default terms in legislation, and then let companies provide real contracts, or lobby to change the default rules, if they're too burdensome.