Summary
Bioware’sDragon Agefranchise is full of delicious ethical dilemmas, gray morality, and nuanced characters with good reasons for doing what they do - even if what they do is terrible and unethical. The rich story and deep character motivations make Bioware games, especially theDragon Agefranchise, beloved by fans.
Dragon Age: Inquisitionsets up a difficult ethical quandary in the form of one-timeplayer companion Solasand his plan to destroy the Veil, the artificial construction separating Thedas from the magical world of the Fade - with good reasons to keep it up orpull it down. These are a few reasons why it’s a bad idea to pull down the Veil.

1Possible Consequences For The Blight/Darkspawn
Super Powerful Darkspawn Is A Real Possibility
Although it’s unclear what the relationship between the Blight, Darkspawn, and the Fade is exactly, it’s clear that there is some relationship. The current state of Blights in Thedas is just barely survivable for its people - add in rampant demon attacks, an entirely new way of life, and the total collapse of civilization as the people of Thedas know it, and that’s maybe not true anymore.
Not to mention that the Darkspawn and their Archdemon lords may get a massive power-up if the Veil is torn down. Corypheus was scary enough, but Corypheus and the other Magisters Sidereal with access to super powerful magic are even worse.

2Magic Gets A Power-up
Magic Is Dangerous
In the world of Thedas, magic is considered to be dangerous because of the wide range of effects it can have on both its users and the world around them. More powerful magic after the fall of the Veil inDragon Age: The Veilguardcould have catastrophic unforeseen effects.
Especially because there are likely to be many poorly-trained mages with massively boosted power at their fingertips, leading to global-scale problems.

3It Could Wake Up The Titans
Waking The Stone
The exact relationship between the Titans, immense primal beings of Earth from the deep past of Thedas, and the Fade is unclear - but what is known is that the Titans fell into a deep sleep after the creation of the Veil, utterly transforming the society of the dwarves.
Although at least one Titan woke during the events ofDragon Age: Inquisition’sThe DescentDLC, it’s unclear what a wider wake-up call could mean for dwarves - or indeed the rest of Thedas. Titans were known to have warred once with the ancient elves, suggesting their ambitions and reach may not remain safely inside the Earth.

4Magic For Everyone
Unrestricted Magic Is Dangerous
Although a normal force in the world, magic has powerful effects and its use is often stigmatized, leading to ignorance and suspicion from those who can’t use it. Mage and non-magic relations in Thedas are already strained. The destruction of the Veil is suggested by Solas to result in a much more freely accessible and available magic - theconsequences of whichcould be catastrophic.
Untrained mages with access to reality-altering magic could radically destabilize societies across Thedas, with newer and more brutal ways of waging war - not to mention how it could affect the lives of ordinary people negatively.

5It Could Affect Qunari In Weird Ways
The Blood Of Dragons
Qunari are suggested to be at least partially theproduct of experimentationon elves with dragon blood, a highly magical people, and a highly magical substance. As qunari presumably post-date the construction of the Veil by many centuries, it’s unknown how exactly the qunari would respond to the destruction of the Veil.
Even Solas seems unsure of what could happen. Given that the qunari are already a powerful and chaotic force in Thedas, it seems unwise to pour fuel onto that particular dragonfire with the destruction of the Veil.

6The Fade Is Full Of Demons
Demons Aren’t Good Friends
The Fade is an almost incomprehensible place filled with spirits and demons. AlthoughDragon Age: Inquisitionshows that the line between spirit and demon can be a blurred one, the Fade is nevertheless filled with spirits and demons which can cause major problems for humans - even with the Veil intact.
With the Veil gone and the line between the physical world and the Fade non-existent, demons will have next to no barriers from preying upon helpless mortals. The chaos seen duringInquisitionwould be visited upon Thedas for the rest of time, at a much higher level.

7Freedom For The Evanuris
Very Angry Elven Gods
The reason that Solas created the Veil in the first place was to lock away the elven gods, fearing that they would destroy the world if left unchecked. His plan worked, but with unintended consequences that proved catastrophic for the elven people.
But if Solas succeeds in tearing down the Veil, correcting one mistake, the Evanuris will be let out of their prison. Solas says he has a plan to fix that, but Solas’s previous plans - creating the Veil itself, allowing Corypheus to use his orb - haven’t exactly gone to plan.

8Freedom For The Forgotten Ones
No One Knows Their Names
An ancient enemy of the elven gods, the Forgotten Ones are spoken of rarely and in very vague words - their identities are literally forgotten. Solas, in his guise as Fen’Harel, was said to walk among both groups of elven gods - but even he felt it necessary to lock away the Forgotten Ones behind the Veil.
Tearing down the Veil lets the Forgotten Ones out, with unknown consequences for Thedas. Even if Solas thinks this is a necessary by-product of his plan, Solas has been shown to have questionable perspectives before.

9Humans Might Not Make It
Total Human Collapse
Nobody knows exactly where humans come from, or why they exist, in the world of Thedas. There are suggestions that humans didn’t appear until after the creation of the Veil, which could mean that humans are incompatible with a Thedas without the Veil.
Whatever the case, a world without the Veil would be radically different, the current human ways of life may be impossible even if humans themselves can persist afterward. The uncertainty is definitely a reason for humans to strongly oppose the destruction of the Veil.

10Destruction Of The Whole World
Genocide On An Unimaginable Scale
Solas himself has said that the world won’t survive the destruction of the Veil, although precisely what he means is unclear. Even if he means the current civilizations won’t be able to survive the transition to the world after reintegration with the Fade, that’s countless peoples and cultures snuffed out, forcibly changed.
In the thousands of years since the Veil was created whole new cultures have flourished, and those civilizations are just as valid as those of the ancients. Their loss would be a massive blow to Thedas, as even if most people don’t die in the chaos, their cultures and way of life will.