People try to run for President who have no business seeking the office. Who wouldn't know what to do when they got there, if they won. Who can't organize a national campaign involving a few thousand professionals, let alone run a superpower. Who've never run a business in their lives, or commanded men, or made important decisions. Or who have whacky, crackpot ideas that even their own side of the ideological spectrum rightly dismiss as tinfoil stuff (the Lyndon LaRouche types, etc).
This sort of thing is not Kerry's problem. Acknowledging that he does not have these sorts of problems does not amount to endorsing the man or voting for him or wanting him to be President. It is elementary fairness, and also maintaining a useful level of scrutiny and seriousness about the most important job there is. Kerry could function as a US President. He could form an administration. It would run the country - maybe in the wrong directions, but not haplessly flailing around, not knowing where any of the buttons are or who to call.
Disagree with the man's policies, criticize his record, attack his whole party's ideology - knock yourself out. I do too. But "unqualified" means something in the context of Presidential politics, and the charge does not fit here. It does not help politically, either, because it focuses attention on the wrong subject. His resume is not weak. His policies are.