*tries not to be cynical*
Huh? Now you've piqued my curiosity.
There are plenty of ways that people can and do take away experiences that have already been enjoyed. They can't take away having enjoyed it, but they can spoil the experience in the future.
Of course, technically speaking you are your own master and can refuse to allow this. But when the evil mastermind reveals that they plotted all along to become your sidekick in order to crush your will, well, being told you should hold onto the happiness of a lie seems a bit impractical.
Like if it's pointed out to you that a really enjoyable experience you had caused unintended pain to someone you care for. Doesn't really take away the experience, but certainly adds unpleasant associations that may make it impossible to freely revisit that experience with a sense of the joy you felt when you were in it.
Which may be all to the good, if a lesson needed to be learned. I'm just sayin'.