You're right. Having customers learn about employees scarfing up hard-to-get items hurts Walmart more than the sale to employees helped them.
Perceived ethos has a value and people already have many reasons to hate Walmart. This just gives them another. Does anyone think Walmart wouldn't take a hit in public opinion if employees were caught snarfing up whatever is the next must have christmas toy before consumers could fight over them? If I were in that position, absolutely I would have a strict policy against that sort of thing.
Doesn't a lot of Walmarts clothing come from sweat shops in 3rd world countries?
Doesn't seem to effect a lot of people.