I understand the sentiment, but I'd caution that the desire to be able to express yourself freely can be seen as cover for having license to say whatever you want without regard to how it effects the other person. This is bad even if you don't intend to use it that way: you should be spending some cycles thinking about how the other person will feel about what you say. I speak from experience: saying what's on my mind has at times been hurtful to people I care about and I should have censored it or redirected the impulse.

Perhaps part of what you're objecting to is not that the person prefers you to lie, but that they prefer a world that can't exist to exist. If this were really what's going on, that would be a severe lapse of rationality. But that world can exist: our opinions are mutable and it's quite possible to decide to like the play. The conversation is actually about something completely different: whether you're willing and able to emphasize the positive over the negative aspects of something for her sake, which is an essential skill in any relationship.

The conversation is also about asking for acknowledgement and approval for something she's worked hard on and probably partially identifies with.

Please note that I'm not saying this is easy or obvious. Empathy is a difficult skill and requires training (or socialization), followed by practice and attention even for those to whom it comes easily.