Conversely, I've seen many televangelists smile as they then plead with you to hand over your last dollar to receive the Lord's blessing. I've seen them smile as they gloriously proclaim that God's judgement will bring down destruction upon a sinful world. I smiled when I told people the Good News of the Gospel, one that at the time I understood to mean that there would be people who would fall short of God's requirements and end up in Hell.
A smile is no indicator of actual happiness, or even an internal ethos sustained by joy. Aesthetics are often used as shorthand to communicate satisfaction, contentment, and peace, where none exists. Some of the kindest people in the world are not often seen smiling, while some of the cruelest, most hateful human beings will paste on a smile and speak softly of their hatred.
I guess I can't knock it, because it works. Look at politicians and preachers who stand at their lecterns and pulpits and smile as they categorically separate humans from their humanity, and other the very people who should be protected the most. A soft word turneth away wrath, but it can also fortify your self-imposed chains.
The aesthetic is a powerful tool.