My Tav was a friend to Gale, and from the outside, I felt like Gale would be better off if he could release his feelings for Mystra and become stronger. In my eyes, Mystra is a traitor who left Gale in the lurch when he needed help the most. She wanted him dead (and the death of everyone else at the same time), made him a "live bomb", and he continued to remember her and wish for her "forgiveness" even afterward. She doesn't deserve the Crown, and perhaps it's better for Gale to really "become an opportunist" and gain power himself. Perhaps I feel this way because I've always enjoyed playing as independent characters who are atheists, and I stand in solidarity with Astarion in his attitude towards the gods (or Astarion's story itself has additionally influenced my attitude towards the gods). Of course, if you look at Gale and Mystra's story not as a couple's relationship but as a "goddess and a misbehaving mortal" story, there would be a different perspective, but isn't that demeaning to Gale himself?
"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. Whether or not to kill the other victims isn't even a question for me because allowing them to have a chance to live is one of the main motivations for not going through with the ritual in the first place."
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. The conversation in the graveyard leaves rather a mournful feeling, to be honest. And the whole subsequent journey with him as well. I can see the anguish on his face whenever the other companions' plots mention power, denial of power, or anything like that. I'm willing to accept that I'm a bad person and let my Tav get a well deserved "evil" badge on her chest, but I don't give a damn about the Gurts and their attitude, if they attack, they get theirs, I care about Astarion's well-being. Yes, I feel sorry for the spawn, and you can rightly reproach me with the fact that "you could have been in Sebastian's place", but everything has its price. The worldview change in the Astarion novel does happen right in the course of the game (it makes me laugh now to remember how naive my Tav was in the first chapter). You can fantasize and imagine that Tav and Astarion (or Gale and Astarion, as in your case) will find other ways of doing things if they refuse Ascension, but unfortunately those ways aren't in the game itself.
