The insight check that Astarion isn't really in his right mind during that battle, along with all those people in the dungeons, made it quite easy for me to convince him to step down from the ritual.
For me, that was the only motivation at all (although I can't argue with those who point out that those 7000 spawns can do a lot of evil). But now I see this check as just a trap, a snare for Astarion and an overly naive Tav. Because I need assurance for Astarion, not hope.
I actually see it differently. The narrator talks about his fear, which we know is his motivator from the start of the game - nothing new there. She also mentions the smell of blood and the promise of power being close as intoxicating to him. These are things he loves, and having them makes him feel good. While he may be a bit fixated on them in that moment, ultimately it doesn't change the fact that this is what he's been going for all along. Even if there was no blood around, he'd still want to ascend. He's plotted and waited for that moment to happen, so of course he's feeling elated when he can finally enact it. To me it just makes him more determined and aggressive in that instance. He can perfectly articulate counterarguments to Tav's objections and suggestions. If you fail a persuasion check he will also say how he doesn't want to live a crappy half-life. He knows exactly what is at stake. He sees the power of the ritual and the freedom it will grant him. He's coherent, rational and pragmatic, therefore he can think clearly.
The more you learn the facts, the longer you play the game, the clearer it becomes that Ascension for Astarion is his only real path. And the rejection option is just a trap.
I would personally call it his fated path, because it really seems like his destiny. Having lost everything, rejected by the gods and then through a seemingly coincidental turn of events he gets a one in a lifetime chance to succeed and take everything from his master and despite all odds he rises to the top in the end. It makes for a great story.
Instead of being helped by the gods, he is helped by the devils - first Raphael and then he receives Mephistopheles' blessing. Even when he is in hell he mentions he feels at home in there. Sometimes it makes me wonder if his ascension was some diabolical plan all along.
It it also the logical outcome. There are all these bits here and there where it's clear that he is trying to lure the MC to the dark side, and convince them that power is something they should both strive for and enjoy together. I'll mention the most memorable scenes I could quickly go back to.
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It starts with the bite scene when he almost kills you: 'And look what you've gained. Together we can take on the world.'
He considers the tadpole as valuable power and a gift and encourages you to use it and embrace the abilities it grants you.
Before getting to Moonrise Towers he says 'You know, I feel a connection between us. Like we're two souls walking the same path. Whoever's waiting for us at Moonrise Towers controls it all. But if we can take that control from them, imagine the power we'd wield. Imagine, the entire cult under our thumb. If we can control the tadpoles, we can keep ourselves safe and enjoy a little world domination on the side.'
Once he learns of the ritual, he focuses on that instead and starts imagining himself as a lord and Tav as his consort, though the latter can only be read between the lines at first.
When he talks about Cazador's ritual: 'This may be a beginning, not an end. I can see myself now. Lord, King,
Master. We'll be glorious both, you and I. You'll have your day, too.'
After meeting Dalyria and Petras: 'We have to face him and take that power for ourselves. Technically only I will ascend and gain the ritual's power. But we're a team. If I become all-powerful, then we become all-powerful. Nothing would make me happier.'
After getting attacked by his family: 'We aren't like them. We are
better.' (This one in particular makes it sound like he already sees Tav as a vampire.)
After ascension: 'Everything will be ours. Everything.'
After killing the Gur: 'Who better to test these new powers on? And who better to be standing by my side than you, who helped me get them?'
When trying to convince Tav to become a vampire: You're the one that I want, the one that I love. And you could be so much more. We could be together for eternity, ruling this world side by side. We could have it all.'
After Tav has joined him: 'First we'll take Baldur's Gate. Then we'll take the world. We'll dominate it until the sun itself melts, and then we'll give ourselves to the night.'
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Everything is basicly leading to the ascension and Tav becoming a vampire. Rejecting it isn't just an alternative choice but it is also going against the whole plot setup. To me it's also rejecting Astarion's dark nature and wanting him to be more human, instead of a vampire that he is. There's a reason why he seems so broken and unnatural. It's because he doesn't know what to do at that point. His dream life is no longer possible. When he invites Tav out he says he is
reassessing what he wants, meaning he wanted something else initially. He's in cope mode. Maybe that's why you feel mournful about the graveyard scene.
It's pretty much this: Spawn = Astarion lite for more sensitive people, and Ascendant = full Astarion experience for the daring ones.
No ritual is a perfectly valid path of course, but I think Larian did both Astarion and the players dirty in that scenario (there's also a whole thread about it), and I wish they made it better.
