well.... I don't like to get into the label game of whether I am or am not a libertarian, I do have many such symptahies though.
That said.... there is respected....and there is respected.
On its face, it is hard to argue with such terms without also arguing with other kinds of NDAs which, while I tend to not be a fan of, I am not really dead set against either. In fact, I can only find one reason split that hair, but I do think its a decent reason.... bad reviews are a form of consumer protection and so they are actually asking you to cover up their quality so as to reduce other people's ability to make an informed decision. As such, I would generally be ok with saying.
That said, I should also point out that one has generally already paid by the time one writes a bad review. If they wanted to charge you, they would have to do it after the fact.
As such, I would say, I am ok with them having this policy and not ok with the force of the state being used to enforce its terms. So feel free to charge me $500, I am not going to pay, and i will never come to your establishment again, you can grow old and die thinking I owe you $500 for all I care. Enjoy your policy.
Hows that for libertarian?