I feel like this dialogue was just poorly phrased. It should be more like:
Inquisitor: You'd murder countless people?
Solas: How many have you killed to save your own? For your world?
The way its currently phrased, its too easy to argue against.
And the Inquisitor has certainly killed many. And lets not get hung over semantics like "murder".
The difference between "murder" and "defense" is hardly semantics. My Inquisitor wouldn't have killed a single red templar, venatori, etc, if they weren't trying to kill her and hers' first. But they were.
Solas is not doing the same thing. We aren't attacking him and his people. I'd help him and his people if he'd let me, on the condition that that help not require the death of me and mine.
As far as we're aware of, the ancient elves that may still be in stasis or something could theoretically live in the current Thedas if awoken. They just wouldn't be immortal or as magically inclined (though all still magical to some extent if the Sentinels are an example to go by.) Solas just doesn't currently consider that a life worth living. He considers those things that are missing to be intrinsic parts of his people that he took away and his guilt and pride won't let him stop at just letting them live, but insists he restore what he took.
If there's a way to do this without hurting others, I'd be fine with it. But he needs to either find/be shown that other way, or he needs to learn to accept that **** happens and the world changes and learn that how things were in the past isn't the only measure of how they should be in the future. Learn to adapt, in other words. If he can't do either of those things, if I can't help him do those things, then we're at an impasse and I have to choose btwn him and the innocents I have a responsibility to protect from him.
And I'll have to choose to protect. And I'll be very sad for it, but I won't have a choice. Duty before personal feelings. (So, basically, I'll be in his shoes at that point, from his distorted pov.)
I really hope there is a way to redeem and save Solas from himself. And I hope its a coherent one that makes sense with all characterizations involved. In my more pessemistic moments, I worry Weekes has written himself into a corner here.