Thy don't care. They know they'e more likely to survive the turmoil (wealth and positions of power have their advantages. Further, may (like Obama) are utter ideologues, and see the loss of 30-50 million souls as an acceptable price to pay to bring about the changes they want.
Further, they will have NO hesitation to use overwhelming force against Americans, despite their urgings of "proportional force" abroad. Their voters won't see any problem with it, either. They'll smugly retort that the gun-lovers should love the massive weaponry being used against them. "Live by the gun", etc etc.
If it gets started, the cruelty and evil that will be unleashed on both sides will compare equally with NanKing's Rape, Cambodia's Killing Fields, and Africa's constant tribal butchery. There will be no rules, no relief, and no mercy... and the rest of the world will wait for their chance to pick up some gains at our expense if they can. (Alaska goes to Russia, Hawaii becomes Chinese, the Southwest becomes Aztlan?)
The evil that will befall us if we capitulate is far worse.
Or do we need to run down histories attempts at disarmed genocide?