Imagine that you're part of a society where one small group of people enjoys special privileges over the vast majority. Let's say, for the sake of argument, that you had the balls to stand up to them, saying that everyone should enjoy the same political equality and everyone should be able to think for themselves. This might sound familiar, because those are essentially what democracy is all about.
This is what's happening in Numbers, Chapter 16. Except in Numbers, the folks with the democratic mentality are portrayed as the bad guys.
It's kind of like the American Revolution, from the perspective of the British. The simple fact of the matter is any human being can recognize when people are being treated unfairly, and when that happens, people get pissed off.
The rebels approach Moses and Aaron with the same gripe the last few people had, except with a much more indepth speech.
Two rebels named Abiram and Dathan say, "Isn't it enough that you us took out of Egypt to die here in this desert? Now, you want to make yourselves rulers over the people? You have not even brought us to this promised land of milk and honey. Do you think you can hoodwink us?"
In response, Moses talks to Yahweh, and then tells the rebels to meet him tomorrow at the Tabernacle with incense. Whoa, incense!?! Remember what happened to Aaron's sons? I smell a trap.
Sure enough, God has arranged to smite all these rebels, by having the Earth swallow them up and send them alive to "Sheol". Because of their courage (since they should've known what happens to complainers), and also because of their well-reasoned argument, the Skeptics Annotated Bible has called them the first "Freethought Martyrs".