IMHO, it was less a matter of rudeness than a continued effort to cover up for the entire legacy of lying, of which Matthews himself is a part.
I would have responsed, "Chris, more than 1 million Vietnamese have immigrated to America since 1975, yet their newspapers are calling Kerry a traitor regarding his VVAW activities. Why is that?"
Yeah, I agree. I always detect a bit of guilt on Chris' part when he starts these conversations. I think he's hoping that voters will look at Kerry as someone who's 'died' for the sins of Chris and the other liberals who fled the country rather than go to Vietnam.