I would love to say that I would go against a crazy plan that would bring about the ruin of the world with Solas ... but I like shiny red buttons. So, I would do it and pretend I wasn't just manipulated into pulling the trigger on extinction-level event. Of course that wouldn't be a canon PT, but it would definitely be my first.
I don't trust Solas. I don't necessarily believe Solas. I'm not even sure he is a good person and not the craftiest Pride demon of all time. But dammit I'd lay the world to waste if it meant more dialogue from him. Also to see his plan.
I think his intentions are good, but his methods may be terribly bad.
I would argue he's a mostly good, if arrogant, person. Go around doing good deeds with Solas in your party and watch him give you approval right and left for it.
But he's depressed, lonely, and desperate. I don't think he's really in a state to be making the best decisions.
Edited to add: If he's a pride demon, then I want to know why he's tossing me approval for doing good deeds all the time.
I think he might be similar to a spirit/demon in some ways. As others have suggested, he may somehow be fused with a powerful spirit of wisdom, or something more powerful than a standard spirit that also embodies wisdom. As we know from Solas himself, wisdom corrupts into pride.
If he's a spirit, too, or something like it... maybe he knows he was corrupted and like Cole wants to change back? It would make sense in the context of his conversation with the Inquisitor and Varric during Cole's personal quest. Changing the nature of a thing is wishful thinking. Until it isn't.