I agree with you, hanny.
Find a better place to give your money to; if no-one ever bought fish at Walmart, they'd soon stop stocking them.
But, of course, it's up to you and your conscience to decide.
I doubt very much if the cories at Walmart are sexed; cories aren't that easy to tell apart at the best of times, so I'd be 99% sure they'd sell a mixture of males and females.