I don't think it would have been harsh, even for a 24th century human.
....Even in the 24th century people will have their preferences, no amount of enlightening will change that. Beverly is heterosexual--granted there may have been that one night at Dance Camp, but she was young and keen to experiment--so she is only interested in relationships with men.
When Worf told Beverly the new host had arrived, she said, send him in'.
She was all smiles until she saw the new host was a female. Then her smile dropped and her attitude changed. She was clearly expecting a male.
It might have been a harsh thing for Beverly, because it might have hurt the perception of her being an enlightened, open minded 24th century woman.
Because of this, Beverly Crusher can be seen being disappointed that the new host wasn't a male. She can call off the relationship.
Beverly Crusher can give a speech about the limits of love.
But Beverly Crusher can not been seen saying that she doesn't like females and that she's only into males.
Even though it her preference, and her right, it would affect the perception of how 24th century humans are--
Catch 22
I'm really not following you here. All I took the scene to be was that she's straight, she's disappointed the new host is female (or, as I said elsewhere, disappointed that it was not the host she fell in love with), and she gave a wandering and self-conscious speech about how she is sorry, I don't love you anymore, wish I could.