You could go to all the effort in the world to make your negative review as fair and as least hurtful as possible, but still offend the prossie or her fluffy fanboys. Some just see the word negative and are instantly offended, and any sense of logical discourse of the more finite points goes out the window.
This isn't a hobby for the fainthearted. If a prossie can't take a bit of online criticism, then how the fuck is she going to be a prossie who see's a range of different men, all of whom will have different personalities, looks, and say all sorts of different things to her, and manage to keep a level head with each punter, providing as good a service as possible to every punter?
Some things in life just are what they are. The benefits of UKP reviews far outweigh the possible downsides IMO. Would sooner have an easily offended prossie retire than possibly have a bad encounter with one. If it means less choice, then that's just the way it goes really. Unfortunate, but I blame the prossies with the bad attitudes for that, not the reviews.