I am convinced that I am not going to vote for any of the Democratic front-runners.
Not voting for Edwards and Clinton is a no-brainer. There are many reason not to vote for them, but all of them pale in comparison to the fundamental reason: They voted for the war in Iraq. Even po' little me knew just by reading the newspaper that the Iraq-WMD connection and the Iraq-9/11 connection were both a complete crock of shit. Either Edwards and Clinton believed Bush, in which case they don't have the intelligence of a under-watered house plant, or they knew it was a crock of shit and voted for it anyway, making them complicit in a crime against humanity.
Obama did not hold Federal office in 2002, so this criterion does not apply. However, he has been a Senator since 2005 and he has failed to use the power of his position against the Iraq war. Where was the grandstanding? Where were the stands on principle? And, most importantly, where were the filibusters? It may be justly argued that it's more strategic in the long-term to play it safe as a junior Senator, but that argument cuts both ways, and it is certainly not playing it safe to run for President.
In other circumstances I'd be inclined to overlook a degree of venality, calculation, and even error—these are politicians after all—but we're talking about a war of aggression, the third most heinous crime against humanity (after genocide and slavery), and the mass murder of what may be almost a million human beings.
Furthermore, all three candidates support a war against Iran, which will again be a crime against humanity and entail the mass murder of thousands, if not millions, of Iranian citizens.
And I am not willing to overlook mass murder. Period. End of story. No mass murderer will ever get my vote, regardless of the consequences.
The leading Democratic candidates, indeed most of the Democratic party, have traded away the principled stance against mass murder, aggressive war, torture, arbitrary detention without trial, electoral fraud, and mopery on the high seas. In return they have gained not even temporary electoral success, but merely the illusion of such success: Those who oppose civilized limitations on our government will still vote Republican, and those who support civilized limitations should never vote for those who will not make sacrifices to protect them.