Law protects "order". That mostly means "protects the interests of the rich". Sure, avoiding rampant crime to the point that it's an obstruction to commerce is the cops job. Stopping the mugger/killer/rapist that's attacking you personally isn't.
If the cops have a choice of stopping 2 crimes or the crime happening to you, they're going to choose the 2 crimes. Presumably you and definitely I would choose to prevent the crimes happening to ourselves. Thus, self defense.
If the cops have a choice of stopping 2 crimes or the crime happening to you, they're going to choose the 2 crimes. Presumably you and definitely I would choose to prevent the crimes happening to ourselves. Thus, self defense.