Solas is one of the greatest philanthropist and saints Thedas ever had.
You don't even know his real history and you're making deductions about his character. You think you know the character because of a short-lived relationship in Inquisition, but you don't know jack about him.
What happened in Arlathan? Did you actually see any game cutscene that gave you an accurate depiction of what Solas was doing back then? Or do you hang on his word to have any knowledge about the truth?
Perhaps you are you speculating based on the heartwarming story he tells you by the end of Trespasser, of how he tried to defend the poor elven slaves from the evil tyrant rulers and on the few bits of info you see at HIS temple - HIS temple, therefore a place that tells a version of history that favors his image and conveniently forgets the wrong things he's done - that obviously paint him as a liberator and hero.
All you DO know is that he was involved with Flemeth somehow - you don't even know what happened between them; were they lovers? master and servant? family? - and that he freed those slaves for some reason. You don't even know who or what the Evanuris were, or if they even deserved the fate Solas gave them.
What if he freed those slaves because he thought he could be a better ruler? What if his goal was to rule Arlathan alone? What if he sought Flemeth to help him accomplish this goal, since she seemed to oppose the rule of the Evanuris and was cunning and poweful enough to face them, sparing him the trouble of openly antagonizing them?
Suppose that is the truth. He wasn't a benevolent soul and a philantropist, then. He was an opportunist who cleverly built an army composed of the same people who once served his enemies and turned them against the kings and queens that would crush him should he fight them on his own.
WE, the players, know nothing of Solas' true past and his intentions. All we know is that he's willing to overlook GRAVE consequences to MILLIONS OF INNOCENTS, people who don't deserve IN ANY WAY what's coming to them, in order to satisfy a selfish want: bring back Arlathan, the elven empire based on slavery and blood sacrifices for rulers like Falon'Din.
Is that a better reality than what Thedas is now? Or is Solas merely going to reboot the world and cause civilisation to devolve thousands of years?
Addendum: His alias is Dread Wolf, the Trickster, who walked among Gods and Forgotten Ones alike. For someone to become known as a deceiver of Gods and "Demons" is quite an accomplishment.
But then again, he DID fool your Inquisitor all along and made it look as though he was helping you when all he cared about was recovering the elven orb.
Should he have succeeded, the world would've been immediately destroyed as he lifted the Veil. And your Inquisitor would be dead seconds after defeating Corypheus and doing HIS dirty work for him.
And yet people like you readily jump to his defense... are you sure you're seeing his real face? Not the façade he so cleverly wears?