I'm sorry, I would like to agree with you and Pie, because it's such a cool opinion, but maybe because I'm a silly fangirl, I can't see Snape as a mean person. I really can't see it. He's snarky, he killed Dumbledore, he indirectly caused James's and Lily's deaths, but he's not evil. I don't believe he has killed anyone besides Dumbledore (which he did on Dumbledore's request, of course ;-), and since James's and Lily's deaths he regretted having joined the DEs. That's how I see it. Of course I might be wrong, because, frankly, we don't know much about Snape, and even less about Regulus. That's why it's easier to find excuses for them and not for Draco - because we know a lot more about Draco's story and behaviour.