Blame the government. They are the gatekeepers that choose to allow this type of pollution.
It is Walmart – not the government – which pollutes in somebody else's garden. And North American consumers are certainly to blame as well for shopping at Walmart and thus contributing to increase its clout.
If consumers could see the details of the whole supply chain (from collecting the raw materials all the way to putting the product on the shelf), companies with no concerns other than maximizing profits – like Walmart – would lose their customers in no time.