He punishes no one. He lures them into the same afterlife that will be his eternal punishment. Is he good? He is the antithesis of good. He doesn't even want the company, he just hates God and therefore, us.
It's not that Satan punishes people, but that he torments them, and enjoys it. Satan loves to see people suffer. God is the one that punishes people, and it pains him more than nails through his hands and being hung on a cross.
