His redemption arc if you care about your companions generally, and influence his choices in his own quest to not become Cazador Mark 2, definitely deserves much better from the game than being the butt of a very poor taste joke.
Necromancy of Thay book gives obvious clues that there was something cut from the game to have an option to cure Astarion as an alternative ending to his quest line, they failed to cut it entirely as he is the one member of the party that wants you to let him read it and has follow up dialogues about it if you do, especially as you find something in Sorcerous Sundries which is supposed to translate it and which currently goes nowhere particularly important.
