Comrade Korach

It seems that Korach was the first communist. It is interesting to interpret the psukim along those lines:
"Korach and his crowd attacked Moshe and Aharon, and said, 'You have taken too much! The whole nation is holy, and Hashem is amongst them - why do you raise yourself above them?' " In other words, they were complaining that everyone should be equal, and there should be nothing differentiating one person from another - the basic premise of every Utopian plan.
Moshe answered, "Tomorrow morning, Hashem will let us know who is his and holy and bring them close to him, and he will bring close the ones he chooses. Do this: Tomorrow, take pans and burn incense upon them in front of Hashem, and the ones who Hashem chooses are the holy ones - you have taken too much, sons of Levi!"
Moshe was challenging their core beliefs. He was telling them that man's place in this world is not inherently equal (although it is fair). He told them that the only way that he and they would be able to decide their conflict would be by taking part in a test whose results would leave a clear winner and loser - something inimical to their stated beliefs! That's why he concluded, "You have taken too much, sons of Levi!" because by them accepting his challenge, they were admitting to the hypocrisy of their own views.
After that line of reasoning didn't work - as they accepted his challenge - Moshe tried a different tactic to forestall the conflict.
"Listen, sons of Levi: Isn't it enough that Hashem separated your entire tribe from the rest of the nation, and brought you close to him to perform the duties of the Mishkan and to stand in front of the Jewish Nation to serve them - Hashem brought you and the entire Tribe of Levi close to him - and you still want the Priest-hood?"
He was telling them that now that they admitted (by accepting his challenge) that there are various levels - winners, losers and some more besides - they should look honestly at themselves, and realize that they were doing quite well performing a select function in Judaism.
"Therefore, you and your cohorts are attacking Hashem - not Aharon, for what is he in this decision that you should attack him?"
If they wouldn't admit to being part of an exalted part of Israel, then Moshe would be forced to come to the conclusion that it wasn't Moshe and Aharon they were attacking, because that position was given to them by Hashem - he could only conclude that they were attacking Hashem!
Moshe summoned Dasan and Avirom to come before him in the hopes that they would see the reason in his words and mend their ways. They answered him, "Not only did you take us out of the wonderful land of Egypt, but you persist in ruling over us! You didn't fulfill your promise to bring us to the Promised Land and conquer it for us!"
Their point was that their attack was specifically against Moshe, and that they wouldn't concede his point that they were attacking Hashem. Moshe, angered by their self-imposed blindness, said to Hashem:
"Don't accept their incense tomorrow - I have not accepted a gift from any of them, nor wronged them in any way." He was saying that although there would be room to have mercy on Korach and his cronies if their attacks were only against Moshe and Aharon (although this is hard for us to understand, remember that Moshe was anav m'kol adam), but since their attacks were really against Hashem, contrary to their stated arguments (as there was no real reason for them to be angry at him, as he had not wronged them in any way), Hashem shouldn't have pity on them and should not accept their offering.

There's a lesson here - many times we see someone do something that he or she says is for a good purpose, l'shem shamayim, while in reality it's a terrible thing that they're doing. It is not necessarily the case that they know they're doing wrong, most likely they are blinding themselves to the truth. Korach and his band were all great men before their downfall - it doesn't make sense that such people should attack Hashem - but they blinded themselves to the true import of their actions, and were convinced they were doing the right thing. A friend of mine used to say (as he was beating me in chess), "When in doubt, think!" As the pasuk says, Ashrei adam m'fached tamid - lucky is the man who is always in doubt - because he is the one who thinks!