Peter, it's a cultural thing: North Americans behave differently from central Europeans in this respect. Effectively it boils down to perception of "politeness." Responses you may perceive as impolite may be perceived by others as entirely appropriate, and vice versa. IMHO the appropriate response on both sides of the Atlantic is to ignore any perceived petty insults to focus relentlessly on substantive issues. People either respond in kind in which case you can have a useful discussion, or they don't. C'est la vie.
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1