An armed law abiding citizen is the only thing they are afraid of. It gets in the way of thier want, need and ability for total control.
They despise legally armed citizens because their existence is a bold statement that the Constitution means something, and citizens have some level of independence from the State. As Machiavelli said:
“Because there is nothing proportionate between the armed and the unarmed; and it is not reasonable that he who is armed should yield obedience willingly to him who is unarmed, or that the unarmed man should be secure among armed servants.”