The pertinent argument is that just because Kerry agreed that Saddam was "a threat", had to be "dealt with", etc..., does not mean that he would have kicked the inspectors out, told the U.N. and most of our biggest traditional allies to go "F" themselves, and rushed on in with a terrible and/or non-existent plan of how to run the occupation.
There are plenty of other ways to deal w/ "a threat", as Bush himself has shown w/ N. Korea and Iran. (Both real threats, FWIW). The problem is that this logical conclusion does not fit w the current climate of debate, which is pretty pathetic if you ask me.