I think he misspoke and it went downhill from there. I think for Kerry it was easy for him to make the error, because I think in his heart of hearts he really believes that those in the military are dumb, but I don't think he intended to say it.
The Leftie-Dem idea of "supporting the troops" is to recast them as hapless victims. Obviously men and women only enlist because they have no other options. Therefore, they are to be pitied. This is so ingrained that they forget other people don't think this way.