The point of trademark law is to prevent someone else from exploiting a company's investment in branding. For example, preventing Joe's Corner store from renaming themselves as "WalMarts". The law should NOT be used to protect Wal-Mart from criticism (Wal-Mart Sucks!) or even to prevent a competitor from using the Wal-Mart name and trademark appropriately (Shop at Joe's Corner Store because we pay our employees a decent wage, unlike those pricks at Wal-Mart!"). In other words, the law should protect against the theft of intellectual property, not against free speech.
Walmart is infamous for all kinds of human rights abuses.