Some people on the right end of the political spectrum have suggested that if you disagree with the Iraq War, you shouldn't say anything. I think there's a kernel of truth in this, in that if such talk was widespread and widely reported, it would have the effect of discouraging our troops and encouraging our enemies. But ultimately, to suggest that people should keep their opinions to themselves goes against the whole spirit of freedom of speech and expression.
On the other hand, some people on the left end of the political spectrum have reacted to this by saying that dissent is the highest form of patriotism. This is just silly. Dissent is not the highest form of patriotism. Children dissent when they scream "NOOOO!" It doesn't take any allegiance to one's country, community, or family to simply disagree. Rather defending the right of those you disagree with to dissent is one of the highest forms of patriotism, because it puts the group that you and the dissenter belong to on a higher level than just yourself. By defending the right of others to disagree with you, you are standing up for their right to be free rather than insisting on your own way.