Actually, the evil damper limits the amount of evil allowed to escape. Basically it limits how evil what we are looking at can be. Satan and company really look like the scary stuff we see when the dampers are off. They use the dampers to keep from givin everyone a heart attack. When they are turned on, everybody, Satan and company included, see hell as the bland office environment we usually see. Tho the lake of fire is still there, it's not evil, it's just... fire.