A white knight is generally someone who will defend/comes to the aid of a person no matter the scenario. Often clouded by their own personal feelings towards said person. So in these scenarios, a lot of guys will become white knights if they had good experience/are infatuated with a certain SP and feel the need to defend any negative comments towards them. Which I try to reason with a previous post I made that every SP is human and can't always provide the same level of service, also some guys have different things they look for/get turned off in SP's which can offer negative reviews.
Just pointing out someone being unreasonable (himself being drunk, expecting services not offered etc....) in their review doesn't make one a white knight.