Make no mistake, this is perfectly legal. The comic-shop proprietors would be destroying their own property, and it is their right so to do. However, this seems little different than someone buying books to burn them.

They would destroy a work of literature with the express intention of preventing another person from reading it. Anyone who does this is engaging in censorship, and Marvel Comics is agent provocateur.

This is not the first time Marvel Comics has tried this, and, according to them, previous efforts have netted tens of thousands of covers.