The optics of going door to door gunning down white separatist is better than the images of collateral damage that would come out of cops storming a school. I'm afraid the cops would go door to door in a heartbeat. After all, there will be no real danger to them. They can come charging up in their MRAPs, set up a perimeter, issue a call for surrender though a bullhorn, then engage in a little 12 on 1 fun with their fully automatic weapons.
It's not like the cops are going to face the resistance of a whole pro gun neighborhood organizing against them. And even if they did, they could just hunker down in their MRAP and use it like a pillbox. Who's got an anti-tank rocket lying around to level (so to speak) the playing field.