I like to think that Sarek was cautious over them, at least having a grasp on the fact that the Cardassians were brutal and militaristic and couldn't be reasoned with, and probably saw war as a logical conclusion to tensions between the Federation and the Cardassians, while Spock probably took the Starfleet Gospel to heart and thought they could be talked into being peaceful and nice. Since we all know how this ended, it's possible Sarek was not only offended by the fact his son insulted him in public, but dared to oppose his father, since he was in the right.
It's also interesting to consider the Cardassian situation juxtaposed with Spock's prior experiences with the Klingons and his future efforts to reunify the Vulcan and Romulan peoples. It's not all hard to imagine Spock envisioning a scenario in which the Federation could find a way to peacefully coexist with the Cardassians as they did with the Klingons, particularly given the pivotal role he played in the peace process with the latter. It's also not hard to imagine Sarek scoffing at the idea and attributing Spock's optimism to his emotional human half--a comment that would almost certainly have infuriated Spock and driven him to attack his father publicly.
--Sran
Although it's the Vulcans that are supposed to be more pacifist, as Surak taught peace and as we saw in "savage curtain," always favored non-violent and diplomatic means to resolve conflict. Spock would actually be closer to the "full Vulcan" position if that was his view.