I see other people have posted good explanations, but I think the simplest explanation has to do with how you break down numbers. Lets take a number, say, 124. We can rewrite it as 100 + 20 + 4 and we can rewrite that as 1 * 10^2 + 2 * 10^1 + 4 * 10^0 and I think you can see why anything raised to the 0th power has to equal 1. Numbers and math wouldn't work if it didn't.
Unfortunately this doesn't really faze Christians at all because many of them believe that God is the source of all that is good, and so by default anyone who worships God is also good by default, and of course this logic follows that anyone that doesn't worship God is evil by default.
Also, barring that, just because Satan punishes bad people doesn't make him good. He punishes bad people because he's jealous of God's love for Humans, and he hates them for it. He's more of an antihero I guess if you really wanted to paint him in a somewhat good light.