Not when all your options are ****, since separating the fade was the least destructive outcome compared to just letting the elven gods raze the planet to the ground. Understanding the world does not stop the people from it to screw things over.
The consequences of Solas raising the Veil is an example of unintended consequences even as they're a demonstration that he doesn't understand the world. But, because they were unintended and unknown, that is a mitigating factor- not an excusing one, but a mitigating one. As if the fact that god-tyrants were already procuring abilities (like the Blight) that could have destroyed the world. There were costs, but they were unknown at the time, and arguably not as severe as the alternative. This is why I do not lambast Solas for what he did in the past compared to what he intends to do in the present, except to point out the fallible nature of his intent.
Solas tearing down the Veil, on the other hand, has no such mitigating factors. The Veil is a limiting factor, not the enabler, of god-tyrants destroying the world for everyone else. The consequences are known. The needs and wellbeing of the many are not being served by tearing it down.
No. Moral sanity is subjective. Morality is an human concept and human beings are the most flawed creatures in the world. Our flaws don't allow us to dictate what is absolute when it comes to morality.
Moral sanity is a subjective, but a collective subjective. Our flaws don't allow us individually dictate what is absolute, but our culture allows us to come to a consensus about what is and is not morally acceptable. Extreme outliers- such as those that think mass genocide of people who don't see the world as they do is acceptable- can be identified for the deviants they are. That subjectivity comes not from them being deviant, but what the consensus was: Solas's genocide ambition would be morally defensible (or at least morally non-insane) if there was a signficiant consensus that genocide-because-personal-preference was a morally righteous thing.
If you wish to disregard basic morality in defending Solas, feel free to do so- but an appeal for ammorality, in defense of immorality, is one that no one else has to accept.
For example, if killing 80% of the human population on earth gave us the guarantee that future generations would be able to live in a utopic lifestyle indefinitely, wouldn't that be better then letting everyone live at the cost of constant threath of extinction brought by overpopulation, war, famine and destruction of our natural resources to supply the masses? Some times, there no easy answers.
Sometimes there aren't. In this case there is.
Solas is not offering future generations a utopic lifestyle indefinitely. Forget a guarantee, he's not even suggesting he has a solution to overpopulation, war, famine, destruction of natural resources, or threat of death or extinction. He is promising to deliver all of that, in an attempt to bring back a past era where all of that still applied.