Copperheads aren't aggressive, they're docile mostly. Cottonmouths CAN be aggressive, IF provoked. There is just a fear of snakes that some people will never overcome. So they needlessly kill them.

It is illegal to kill any native wild snake here in TN, but when a former schoolteacher I knew had timber rattlers getting inside her house, I think I would make an exception unless a professional snake handler was handy. My brother was almost bitten in the face spraying for bugs underneath her house once. He had no clue they might be under there.