if elves were spirits before the veil, and this becomes common knowledge whilst Solas puts his plans in place - if Solas fails, won't there be a huge chance of a violent backlash against elves? Likely, many people will argue they're descended from demons, they're the hated children of the maker, and they follow false gods without hesitation. I can imagine people suddenly having no trust in elves - not like they had much before - but they'll look at every poor, hopeless city elf and see a potential traitor, a spy, an evil spirit, an abomination. Even Leliana's "radical" chantry could not avoid condemnation.
I'm afraid some groups - particularly templars, who are almost exclusively human - might attempt genocide. Like, actual genocide, based on racial hatred and fear. Pitchforks and arson attacks and mass killings if they refuse to covert and forced expulsions from their alienages, forcing them out of their home with nothing but the clothes on their back. Regardless of their role in Fen'Harel's uprising - and I imagine most won't be involved in that. Because DEMONS.
If Solas fails, he could inadvertently destroy all the elves he wants to save, for real.