I guess this makes me the first who stands up to be counted firmly on the side of the elves? ^^
I'm slightly sad that that is not actually an option in the game. I mean, I can see why, because any future story writing would become hell if your Inquisitor can potentially be on the side of the antagonist. (especially since the ending kinda makes it look like they'll continue to be around at the very least as an ally of any future protagonist)
Still, it makes an elven Inquisitor feel like a right dork if all the elves are rallying to their people's cause, and you're left behind with the humans.
I know there is the whole genocide thing and all, but... well. For one, it's not specifically said that everyone will die. As far as I can tell, modern elves are not biologically different from ancient ones, so they should be able to connect to the Fade without dying. We don't really know what opening the Veil will do to people, or why it would be so destructive.
It might just be that because everyone believes the Fade to be an evil place full of demons, that is exactly what it will be, and only once everyone who believes it to be so is dead can it become anything else. In that case, Solas rallying the elves might actually be an attempt to save them - teach them not to believe the Fade to be hostile and it won't be, sort of thing.
At any rate, I don't really think Solas can be blamed for thinking the way he does. To him, a world severed from the Fade is obviously a broken one, and he's just trying to heal it. He broke it, he has to fix it, makes sense.
The Tranquil analogy is really quite a good one. Everyone wants to restore the Tranquil's emotions because what was done to them was cruel and wrong. Still, we have to face the fact that restoring their emotions would likely kill the vast majority of them, because they're so over-emotional and unable to control themselves that they're just an Abomination waiting to happen.
If you ask a Tranquil whether they want themselves restored, they'll say no, because it's too dangerous and they're content the way they are. If you ask everyone else, a lot of people (especially everyone who read Anders' manifesto xD) would want to see them all restored regardless, because they consider Tranquility to be so terribly wrong that even death would still be better.
Then consider that Solas is one of the latter people, and finds himself in an entire world populated by Tranquil. You can't really blame him for being horrified and wanting to undo it, despite the damage it would cause.
That said, I'm not too sure about his plan. He does have a history of badly-thought-out plans. And if, as he says, he has a way to deal with the Evanuris (while still removing the Veil), then... why didn't he just use that in the first place and avoid destroying his world altogether?
Another reason to take Solas' side in this might be because it looks like the world is going to get destroyed sooner or later anyway.
As Solas mentions in a piece of banter with Blackwall, the world kind of lives on the assumption that when all the Archdemons are dead, the Blights will end for good. Solas considers that assumption silly, and it is probably safe to assume that once the last Archdemon falls, the Darkspawn will not just disappear. So the only reason the world is reasonably safe from them at the moment is because they're spending all their time digging for Archdemons. This gives Thedas all of two blights' worth of time before the Darkspawn go on an uncontrolled rampage and likely destroy the entire world, because while you can sort of fight off darkspawn armies, there isn't any real way to stop the Taint from spreading.
So, you know, maybe Solas has a point when he says that destroying the world to bring back Elvhenan is the only way. The Darkspawn corruption does originate from the Fade, so maybe whatever Solas is planning might put an end to it.
At any rate, while he may be quite arrogant and zealous at times, he does show a lot of compassion and wisdom throughout the game. If you earn his friendship and possibly love, he has a lot of very good reasons to abandon his plans of destruction, and he does make it quite clear in Trespasser that he wishes he could. That does kind of imply that there is a good reason he keeps doing what he does despite all it costs him and everyone else. We may not understand Solas' reasons, but he knows a lot of things we don't, so perhaps a little trust is in order.
Also, since people seem to have been bringing it up, just clearing this up: "The People" is just a translation of "Elvhen". He is still talking about ancient elves there, despite not saying "My people". And anyway, it would be kind of weird to say "mine" when he's talking to Mythal.