Right off the bat, the story of creation in Genesis describes how God unjustly punishes the serpent for its part in deceiving Eve. The problem with this — clearly — is that the serpent (according to their story) was just an unfortunate host to the Devil (it was possessed, if you like). Therefore, it wasn’t really to blame for its actions.
So since we see that God is not at all what we would call “fair”, does this make the Devil the good guy? No, probably not. The Bible is where our reference comes from, and it doesn’t give Satan much more credit than it does God (yeah, you read that right). I mean, yeah, it paints a horrible picture of God, but the one it paints of Satan is only slightly less malevolent. So, maybe the Bible is really evidence that semi-ancient peoples believed that there is no “good guy”.
You’ve got God wreaking havoc on everything in his path, and using various people and groups of people to bring about his “justice” against others. Then you’ve got this “Devil” who pretty much starts off by saying “Look, God isn’t really being up front with you.” And it turns out he’s right. God was only half telling the truth about the eating/dying thing. So basically, the Devil is this guy who pops up now and then to remind us that God isn’t so “great” as he might have led us to believe. Not that he really gives a damn about us, but he doesn’t want God to get his way (having all these “believers” and what not) simply because the people are ignorant of God’s shady past.
Now supposedly, the Devil has put up with a lot of God’s shit over the millennia, and I guess it’s turned him into a bit of a bastard. So just because he’s telling Eve the truth doesn’t mean he’s her friend. He’s just God’s enemy, and remember: Your enemy’s enemy is NOT necessarily your friend.
So, here’s some truth from the Bible: It is a reminder that wherever there is authority, there is not necessarily justice. Even being the Master of the Universe doesn’t necessarily make you right.
Something that is too often left out of religious/rationalist debates is the question of why people should even want to worship the Christian God. He’s vile beyond belief! Even if the shit about creation and Jesus is true, by offering eternal life, Jesus is only offering a conduit to a fate controlled by the most violent and ruthless dictator imaginable. Jesus did not deny his association with the evil Hebrew deity, Yahweh. In fact, he claimed to be possessed by Yahweh’s Spirit.
Why would anyone who has read any significant portion of the Bible without throwing it away in disgust actually choose to worship (!?) the beast called “God” presented therein? It’s unreasonable to even expect that from anyone. No wonder the Catholics hid the truth from people for so long! They probably had no idea just how gullible (and well-trained) the populace was — to still believe any of it after they could read it for themselves.
So that’s it. Even if there is a God, he is imperfect (as evidenced by his countless errors e.g., creation and its many flaws), and Satan is just the rebel spirit telling you all to get bent, and encouraging you to be on the lookout for any authoritarian bullshit (in case you erroneously seek to find solace in the perilous hands of God).
You’re on your own. Try not to fuck up.