You don't view the relationship as transactional, but the character you're speaking to does and they want to make that clear because it's an important part of his story.
I don't think anyone here has a problem with that. But it should be made clear with Astarion's words, not the player's. The dialogue in question only has the following options: 1. "turn me"; 2. "fuck me"; 3 and 4. "let's argue". There's nothing to pick if your character for example doesn't want anything from him and isn't interested in picking arguments. Astarion's personality doesn't need to change if the player is allowed to say "i don't want anything." He'd just continue pushing and it would be in character.
