But unless you're willing to believe that everyone else in the world, everyone Not Like You, is evil - completely and irredeemably evil - then killing off the entire world is a monstrous and evil thing to do. It's only slightly less monstrous if you're "merely" leaving everyone else to die, as you get in some modern retellings of the story (such as Atlas Shrugged).
If other people are basically just doing their best to get by, then killing them off for their perceived failure(s) isn't noble; it's villainous. It's horrible. And if you discovered that someone was planning to do that, the heroic action would be trying to stop them.
...This has devolved into something of a rant, which wasn't exactly what I intended. So, on a lighter note, here's Bill Cosby with his own distinctive take on the story: