I guess it this must depend on the jurisdiction and the precise rights in question because in the US contracts regularly ask you to give up some of your rights and I'm pretty sure they're enforceable as such.

I found this answer (https://law.stackexchange.com/a/13374) though I cannot advocate for the source reliability, it does corroborate with the little research I did in this matter in which as long as the subject of a contract is under the law, the contract is valid, although this is all in context of the seventh amendment.

I come to believe, therefore if the subject of a contract, in the facebook case information theft and violation of privacy, the contract can be nullified in favour of the citizen

In germany a contract can be null and void (in whole, meaning the contract was never valid to begin with or after the fact, meaning the contract was invalidated) without the contract specifically breaking any single law.

Unconscionability in german law may occur in a Knebelvertrag (oppressive contract) or in contracts that abuse power differences between the contractual parties or even usury (immoral monetary loans for example). In that case the contract can become invalid.

In case of any disagreement, the spirit of a contract weighs harder than the wording in textform, if it is possible to determine.

A contract can also not place any part of the agreement outside the reach of a court (ie via arbitration clauses. You can still fight your agreement outside court but you can't forbid someone from going to court). You can't waive most of your rights either and even if you do, a court may determine that contract to be invalid and the other party having violated a right will then be prosecuted.

Contracts themselves are largely a specific case of a legal transaction (negotium juridicum) and aren't specifically regulated (all above is basically just about any legal transactions ranging from contracts over last wills to verbal agreements).