I do not like electability arguments as they are an argument of weakness and cosmetic salience. I was not a big fan of John Kerry's use of the electability argument in 2004 as his proposition that he was the only Democrat who could beat George W. Bush was later proven to be false as he was unable to create a distinct differentiation on the major issue of the 2004 election, Iraq, and could not parry the expected blows that were thrown at him. If a party has confidence that its basic ideas and prescriptions are both right and reasonably popular, and that it can also offer a fairly wide field of obviously non-batshit insane individuals than the electability argument should not be in play.
I believe that the Democratic Party in this Presidential Cycle has a fairly deep and credible field of obviously not batshit insane candidates. I also believe that the Democratic policy portfolio is fairly popular even as personal popularity of national Congressional Democrats is going downhill due to their inability to implement their publicly preferred agenda.
I also like John Edwards, or at least I want to like him, but when he is trotting out an electability argument in that he could expand the playing field for Democrats into the Deep South while Hillary Clinton due to her gender, and Barrack Obama due to his race implicitly could not do the same. This is an argument of weakness and superficial characteristics --- a drawling white Southern male is attractive to the South, but the Democratic Party does not need to win the South to win a majority as the 2006 Cognressional elections and the current composition of the Congress has proven.
John Edwards has some very good policy positions and an excellent moral center for his campaign. He should embrace the Two America diagnosis and prescription and run with it instead of engaging in such a weak electability argument.
And by the way, Hillary Clinton is beating all of the potential Republican nominees by a significant margin according to Newsweek (h/t AmericaBlog) so besides being a weak argument, it is a wrong argument to make at this time.