Dean Can't Win the General

He would not win a single southern state.  He will not win in the socially-conservative midwestern states (Michigan, Ohio, Pennsylvania).  He will get pounded on the gay marriage issue (Calm down here, I'm not saying that he deserves to be pounded, just facing reality).  He will not hold enough of the Jewish vote due to slips of the tongue on Israel.

In short, he cannot successfully re-assemble Bill Clinton's winning coalition.  

Go with your head, not your heart.