Why are reviews checked before they appear?
Every review is read once before publication to catch personal details, abuse and anything that is not about the trip. Negative reviews are published — being critical is not a reason for removal.
Moderation is about the things that should never be public, not about tone. We take out phone numbers, full names of crew, abuse and content that has nothing to do with the trip.
A one-star review that describes a genuinely poor day goes up. That is the entire point of having reviews.