What possible difference is there between this scene and the one where Spock brutally forces a hapless male guard to open a door the man doesn't want opened, in "A Taste of Armageddon"? Why didn't the other captives rush Spock and beat him on the head with a stool until he bled enough to realize how monstrous it was to violate people that way?
...or forcing his Katra into an unsuspecting McCoy, almost costing the good doctor his sanity and/or life.
I've never liked the "mind rape" label for that scene, since it seems to be used solely because Valeris is female. I do believe that there is a bit of sexism in this view, as many are uncomfortable seeing a woman bullied by the powerful Spock. If that was Admiral Cartwright, or one of the other male conspirators, it would be seen in a much different light.