I've always hated Walmart for that. And you know that the only people purchasing fish from there are probably idiots or kids that will own the fish for two weeks until it dies of starvation or disease. Just the other day, I was there and saw a 9 year old banging on the tanks just because he was bored.
I used to rescue fish from there, and even though my heart is in the right place when I would do that, I was still giving them my business. I boycott the Walmart fish area now