I thought it’s relatively obvious that the ascended ending sets up Astarion as the next Cazador and, in case of a vampire bite, a “master - slave” dynamic (same one Cazador and Astarion had) between Astarion and the player, hence the dialogue options.
The narrative also makes it clear that his story is about abuse (it’s really explicitly stated) and it would be a bit weird to be happy about him never getting out of the abusive circle.
I don’t know what OP’s RP reason was for ascending Astarion, but there are a few answers here, which made me think some people understand the ascended relationship as a consensual sub-dom dynamic, and it’s just not the story.
The problem is not what Astarion's story is about, or how Astarion behaves. Astarion is fine. His storyline is fine. No one is asking for an option to be happy that he's trapped in a cycle (an argument could be made that the player character doesn't even realize Astarion's still stuck in that cycle but since people insist on metagaming everything these days I guess that's not an option lol). Telling Astarion you don't need anything from him rather than starting an argument or asking to be made into a vampire/for sex is not about being happy he's not "free" or whatever. It's about the player's ability to say 'I don't need anything from you', which is a neutral statement that doesn't express any happiness as far as I can tell. If you can tell me why it does, please do in case I'm missing something. Also regardless of what the future dynamic of Astarion and the player is, it should not affect the player's dialogue options yet. Unless the ascension somehow changed them as well and the game failed to mention that, and that's why we don't have a neutral dialogue option here.
The problem people have is that they are being railroaded in how they are allowed to roleplay their character in this situation, namely either being forced to create conflict with him, or either wanting power or asking for sex (which is just... let's say annoying to be civil, after everything with Astarion's storyline). Imagine if you were forced to be mean to spawn Astarion and were forced to ask him for sex or complain about how you'd have preferred he ascends after all; you wouldn't be happy about that, would you? (though the way you're railroaded into being nice to him in that scenario and how you can't break up with him until after the cemetery scene is it's own discussion) It's the same thing here; you do not have an option to say you don't need anything from Astarion, which is what most people talking about this want. It's perfectly fine for Astarion to force you into either breaking up with him to becoming his spawn. It's perfectly fine for him to be toxic if he wants to be (it's also perfectly fine for people to hc the relationship as consensual sub/dom dynamic, and who's to say it's not if you're okay with being bossed around since the game ends the moment the tadpole which keeps the player safe from the whole mind control thing is gone, and we don't see what happens afterwards). What's not perfectly fine is the writers forcing you into playing a specific character after all the freedom you've had so far. All they'd need to do is add a single dialogue option into this one dialogue tree that would still lead to the same conversations it does now (Astarion pressing you into becoming his spawn), and the problem would be solved.
tl;dr: people wanting the option to say 'I don't need anything from you' is not affecting Astarion's storyline or the narrative in anyway, it's a neutral statement that doesn't express happiness, and insisting it does either is kinda weird.
