I get you won't agree with it, but since you asked, here is what the dissent argued (as summarized by Wikipedia):

The Stevens dissent seems to rest on four main points of disagreement: that the Founders would have made the individual right aspect of the Second Amendment express if that was what was intended; that the "militia" preamble and exact phrase "to keep and bear arms" demands the conclusion that the Second Amendment touches on state militia service only; that many lower courts' later "collective-right" reading of the Miller decision constitutes stare decisis, which may only be overturned at great peril; and that the Court has not considered gun-control laws (e.g., the National Firearms Act) unconstitutional. The dissent concludes, "The Court would have us believe that over 200 years ago, the Framers made a choice to limit the tools available to elected officials wishing to regulate civilian uses of weapons.... I could not possibly conclude that the Framers made such a choice."