Yeah, here's the thing...
Those workers, once they have money, are going to spend money. Probably at Walmart.
So Wallyworld would probably be seeing some of that money come back ANYWAYS. Which means that they'd actually make MORE money by paying their workers more, because said workers would actually be able to afford to spend money.
One of the problems with supply-side economics is when the supply-side forgets that the demand-side has to be able to afford what is being supplied.