Because leftists intend to disarm you, impoverish you, imprison you, and kill you.
They've been stacking up bodies by the millions since 1789 to prove they're serious about it.
These same leftists routinely claim machine guns are only good for spraying billets and killing as many people as possible. What law enforcement function requires spraying bullets and killing as many people as possible? When do we need cops to do that? We also hear full auto weapons are only good for war. Well our communities and neighborhoods are not battlefields.