Even a small family is not that easy to support. How much more so a polygamous family - why, even the moslems permit four wifes only to those capable of affording such an establishment.
well, if you look around the houses of Colorado City, you'll see HUGE houses, some of em nicer than the others, but they don't seem to have financial trouble. So if they can afford it, hey, why should anyone forbid em to have such a big family?