Is it that simple? Not really. Not if you want to make it fun and have some sort of logic. But it's no more work than having to develop any religion on any alignment. If I were going to argue about what religions would or would not exist it would be chaotic aligned religions. You need structure and cohesion of laws and beliefs to make it work and a chaotic aligned religion wouldn't have that structure. Alignments are not my favorite thing in the world, but since this discussion began with the alignment terms I have used them.
As for something being evil or good it is often a matter of perspective. Again though, I believe Rob was speaking about the mustache twirling baddie who exists only to cause grief and pain even to those who follow him faithfully. I gotta say there is room in my campaign for such a villainous deity. Why not? I would need to do the work to justify why these people would want to adhere to such a god. I would also need to take into account whether the power of the gods in my world is equal to the number of those who worship him or if they are just incredibly powerful beings who can impose their will onto others.
Let's go for the latter for now. Bronson the Dreadful is an evil god whose power is not dependant on his worshippers. He is a mean tempered, jealous, vengeful son of a bitch. But others find value in following him. An example could be they are an enslaved race and Bronson is a huge fan of revenge, sabotage and mayhem. He inspires this enslaved race to revolt even though they know they might be crushed, but gives them hope. Now Bronson the Dreadful could give two turds in a punchbowl about these people, but because they entertain him he will grant a few powers to make the game more interesting. But to get these powers they must sacrifice their most beloved to him. And some will. And more will if they see those who have sacrificed have succeeded. And as people are, even if no laws or codes exist they will begin to develop them.
There are many reasons why an evil religion can exist. I am not talking about the perspective argument, but the cartoon this is good this is bad version. And it can work. It can add a lot to a campaign. And sometimes it's nice to have a bad guy who makes no bones about it. He stands there with a wide stance, hands on hips, black mustache waxed and curled, dressed all in black and with a sinister cackle he looks at all the land and all the people around him and says, "It is all mine. All mine I tell you. Muhahaha."