I like this idea.
And as soon as I thought that, I paused to consider what sort of person I am.
I guess I’d be happier if I could have healthy, happy, paid workers to collect my wood and stone for me… but if turning spare thralls into construction materials is the best we can get, then that’s what I’d use.
(In the Battlestar Galactica board game, Tom Zarek can turn some of the population resource into food or fuel. Citizen welfare is a concept easily abandoned when conditions turn a little hostile.)