Seems to me one of the fundamental dichotomies of DA is that between order and chaos, with sentient humans/elves/dwarves falling somewhere on the spectrum between the two. Earth/Titans = Order while Spirits/Evanuris = Chaos. So the story of the world, in the larger picture, is the story of these two competing forces, where the height of creativity happens at a happy meeting of the two. How in the heck does this relate to Solas? It does (at least in my head)! Somewhere in the endless parentheses. 
A rough history of Thedas according to this idea (and I swear the idea is relevant to Solas
:
Order and chaos are happily sequestered in their respective realms until some spirits(chaos) decide they'd like to get it on that stability business and jet off to earth, to which the Titans rather strongly object, as the spirits are now mucking up their carefully ordered orderliness. So begins Time and its cycles.
War with Titans-->evanuris become kings then 'gods'-->heyday of Elvhenan, 'dreaming dwarves'-->evanuris war/slave rebellions-->creation of the Veil-->
(chaos) (rising order) (order) (rising chaos) (chaos)
fall of Elvhenan-->ascendance of Tevinter-->Andraste/Chantry-->Dragon Age Events--> fall of the Veil?-->
(chaos) (rising order) (order) (rising chaos) (chaos) (rising order)
Of course, we know more happened during such events as "creation of the Veil", but I think the Vir Dirthara gave us a good glimpse at the gist, and that whether good or bad, it was definitely chaotic. And was also done by Solas. The question is, why?
*firmly secures tinfoil hat*
The cycles of order/chaos are inherent to the existence of the world (as experienced by non-polarized beings). If either side ultimately wins, there is no more creation (as in making, or what Tolkien calls sub-creation). Complete order has no imagination, complete chaos has no substance. Presumably also why the Titans are put to sleep and not destroyed. In any case, if I make the assumption that this view is true (that history is cyclical) and that Solas knows this, it leaves me with the following:
Solas knows that Evanuris are about to bring the world back to the point of utter chaos; perhaps they are willing to destroy the Titans, thinking in their lust for power that it will make them more powerful still. They've murdered the only one of them to keep a sane head. As the voice whispered to the Elves mining in the Deep Roads, "What the Evanuris in their greed could unleash would end us all. Let this place be forgotten. Let no one wake its anger. The People must rise before their false gods destroy them all" Maybe this voice is Solas, maybe Mythal, maybe Geldauran. Dunno. Either way, sans Mythal there's nothing to keep the Evanuris in check. The chaos part of the cycle is coming, but Solas chooses to force it (via creating the Veil) rather than let the Evanuris do so (which may have been chaotic enough to destroy EVERYTHING).
Solas goes sleepy-bye until the next cycle comes close to its conclusion. For those of you wearing ten-inch-thick tinfoil, perhaps the moons were created by Mythal as a calendar to track this very thing, thus the 'eclipse as Fen'Harel stirs'. Anywho. So 'chaos rising' is in effect: the archdemons are almost all dead, the dragons have returned, red lyrium is spreading, the Titans are waking up, the Evanuris may be close to busting out of their prison(s), the dreamers are coming back (Feynriel). Solas knows that madness is about to be unleashed. It's inevitable. What isn't inevitable is how. And now, rather than having a bunch of immortal chaos/order hybrids to pass through the chaos and into the next cycle, he's got a bunch of mortal earthy gremlins with an extremely narrow/short-sighted view and no knowledge. G-RRRR-E-A-T. So, he's now trying to do what he had done before and force the cycle into chaos on his terms.
It sucks, but perhaps he's not wrong that doing so is the best way to control the inevitable fall (as Mythal herself says) and help them fly so they can rebuild. That may even be why he wants the Elvhen proper back, as they are far more capable of going toe to toe with Mage God Kings and Titans and whatever else. Without them, once again, Thedas is screwed. Theoretically, either the Evanuris go on a rampage and destroy everything, or the Titans go on a rampage and destroy everything. And Mythal, knowing this, is not opposed to Solas's plans even (unlike Quizzie) knowing what they entail, such as the loss of "modern" Thedas.
Unless Quizzie can find a way or something. Or stuff. Or whatever. Or 
Long, long story short: Solas and Mythal are/were balance. Perhaps solely because they are wise, powerful, long-sighted, and selfless enough to see it. Solas hates the crap out of it, but is not actually wrong, per se. And that I think/hope that Quizzie can change Solas's how, but not his IF or WHY (cuz he's right on those parts). END RANT.