It's not enough to have language in a contract. There needs to be understanding by both sides about what is being agreed to.
Since the Internet engaged mob-mode before engaging investigation-mode, we don't know how clear these terms are to people who are booking weddings.
It might be very clear because they send an email explicitly telling the bridal party about these terms and asking them to consent, which would also be a signal to the party about the quality of online reviews. Or it might be buried in the middle of 12 other clauses and the customer doesn't know about it.
Obviously there needs to be mutual understanding of a contract for it to be enforced. The original question included the phrase "if I carefully read and then sign that contract," which I think indicates that the contract was mutually understood and agreed upon.
Mutual understanding is not the only ingredient that constitutes an enforceable contract. Issues such as duress, inequality of bargaining position, and in this case, the plain bizarre unreasonableness of the terms, can enter into the equation.
Participation in a contract that specifically covers terms for being slapped also bring with it an expectation of being slapped.