Contracts contrary to personal interests may be found to be contrary to public policy, and voided by the court.
For example, in an American case called In the Matter of Baby M [1988 NJ SC], a woman voluntarily entered into a contract with another couple in which she agreed to be a surrogate mother for the couple for monetary compensation.
After the baby was born, she refused to give the couple the baby. The couple tried to sue for specific performance but failed. The court held that the contract was void as it was against public policy. In a civilized society, there are some things which money cannot buy i.e. taking a baby away from its mother, and thus, against public policy. In certain jurisdiction, it is currently illegal to charge to hire a surrogate mother.
Consider the Assisted Human Reproduction Act, SC 2004, c 2 RSS s.6 (section not yet in force) which reads: (1) No person shall pay consideration to a female person to be a surrogate mother, offer to pay such consideration or advertise that it will be paid; (2) No person shall accept consideration for arranging for the services of a surrogate mother, offer to make such an arrangement for consideration or advertise the arranging of such services; and (3) No person shall pay consideration to another person to arrange for the services of a surrogate mother, offer to pay such consideration or advertise the payment of it.
Parallel language is found in the statutes of other jurisdictions.