The thing is we don't actually know that there is still anything left of Solas' world to bring back. He wants to tear down the Veil, but even he doesn't know what's left on the other side. We've had evidence in DAO, DA2 and Masked Empire of ancient elvhen that did not survive uthenera after all and are just a pile of decomposed bones and pieces of armor in cursed graves now, so what if that's all left of the world Solas remembers is himself? What if there's nothing trapped beyond the Veil but Solas' own nostalgia?
The survavilist logic behind his reasoning can more or less be compared to ours, but he doesn't even know that his plan will accomplish what he wants - for all he knows, tearing down the Veil may just destroy all life in Thedas, without even restoring what's been lost way too long ago to recover. In that respect his mentality is working a lot like Corypheus, trying to restore ye ole ancient times on nostalgia alone, with no actual perspective of success and at the cost of a world that's left them long behind and has evolved too much to be stopped now.
Cole: Stop. You are perfect exactly as you are. But then you turned away. Why?
Solas: I had no choice.
Cole: She feels her face, marked, marred without malice. She didn't know. She thinks it's why you walked away.
Solas: You cannot heal this, Cole. Please, let it go.
Inquisitor: Perhaps Cole can get a better answer from you than I did.
Cole: He hurts, an old pain from before, when everything sang the same. You're real, and it means everyone could be real. It changes everything, but it can't. They sleep, masked in a mirror, hiding, hurting, and to wake them...(gasps) where did it go?
Solas: I apologize, Cole. That is not a pain you can heal.
I think he knows enough to make it worth it. Just like a lot of others are ready to kill him based on...well, not a lot. My point is that he's willing to do what's necessary, even if it kills and doesn't turn out perfect. He's only been awake for a few years. The only real contact he's had with this world is through the Inquisition, so no, he doesn't identify with these people. How many thousands of years did he have to build friendships and bonds with his? These few years are probably mere days to one who has lived for so long.
Should he find a gentler, more peaceful way? Absolutely. I don't agree with him but I understand it. And reading the codex written by Abelas in the Temple of Mythal only makes me that much sadder for the ancient elves.
I have the suspicion that the ones locked away are likely Solas' fellow rebels, who may have had some warning, or those he convinced while he slept. To me he does owe them but maybe it depends on us as individuals. Would I be able to leave people trapped and hurting for eternity to save others I barely know? I'd look for a comprise and failing that...I don't know.
And like his dialogue with Varric:
Solas: How can you be happy surrendering? Knowing that it will all end with you? How can you not fight?
Everything his people were was destroyed by him and now he has the choice to try and bring something of it back, otherwise it will all die with him. Even if it's a slim chance, to him that's better than giving up.
Varric makes hella good arguments in return. Old and new, both too stubborn to find a compromise.
Varric: "We're not our empire. There are tens of thousands of us living up here in the sunlight now and it's not that bad. Life goes on. It's just different than it used to be."
Solas: "And you have no concept of what that difference cost you."
Varric: "Oh, I know what it didn't cost me. I'm still here, even after all those thiags fell."
Solas: "You truly are content to sit in the sun? Never wondering what you could have been? Never fighting back?"
Varric: "You've got it all wrong, Chuckles, this is fighting back."
Solas: "How does passively accepting your fate constitute a fight?"
Varric: "In that story of yours, the fisherman watching the stars, dying alone, you thought he gave up, right?"
Solas: "Yes."
Varric: "But he went on living. He lost everyone but he still got up every morning, he made a life, even if it was alone. That's the world. Everything you build, it tears down. Everything you've got, it takes and it's gone forever. The only choices you get are to lie down and die or keep going. He kept going. That's as close to beating the world as anyone gets."
I love that whole arc of conversation between them because it gives so much insight into how Solas views what he has to do. He can do nothing, let his past be forever lost, and live until that guilt crushes him. Or he can fight back, he can try, which to him is better than doing nothing at all.
His greatest fear is dying alone; alone without his people and his culture. He could try to make a life and find happiness but either way he will never truly be free. Either way he fails. Either way there is more bloodshed. He knows this. Fighting for what he knows wins out in this, instead of accepting what is 'unnatural' and wasn't supposed to be.
It's heartbreaking either way. Or he could stop being so stubborn and just ask Quiz for help. lol *shakes him*