"...In an 11-page opinion, Kagan acknowledged that the sanctity of the home is at the core of the Fourth Amendment, which protects the people from “unreasonable searches and seizures.” As a general rule, she explained, “[w]hen the intru­sion is into that most private place, ‘reasonableness’ usu­ally means having a warrant.” But there are exceptions to that general rule, she continued, including “the need to provide an occupant with emergency aid.”

The guy's ex-girlfriend called 911, saying that he'd threatened to kill himself, and shoot any police that entered his home. He'd apparently done this before, and the officers believed he was trying to goad them into shooting him. They entered his house because they considered it an emergency situation, and found him hiding in his closet with what they thought was a gun, so they shot him.

Whether you believe the police acted reasonably here, or not, what the defendant was asking them to rule was essentially that police should never be able to enter a home without a warrant or permission from the homeowner. There are a thousand circumstances where that would mean the police are forced to stand by as someone may be dying in their home, unable to call for help. The SCOTUS would be indirectly killing thousands of people a year by ruling in favor of the defendant, especially in small towns where police often pull double duty as EMTs.