Contracts don't have to be one sided. They are normally of the same purpose as a prenuptial agreement would be for a nilla marriage. Once the conditions have been agreed upon by both parties, should either side fail to meet the agreement, it gives the person the right to end the relationship, without question or contest.

Another thing to note, BDSM contracts are not legally binding. So you can't negotiate yourself into an abusive relationship. At least not legally.