I'm getting the feeling that Kerry requested the Swift Boat assignment in order to get his "JFK PT-109" ticket punched, in order to use it (like LBJ and JFK) to leverage a run for office.
When he got home, war heroes were out of style, and war protestors were the flavor of the month, so he changed tacks to sail with the new wind.
Now, 40 years later, he's trying to run again as a "noble war hero."
Which was it? Depends on what he wants, at the time.