I do not believe that freedom of speech should be curtailed during wartime. The United States is a democracy and democracies should not do away with their civil liberties simply because there is a war going.
It is, of course, necessary to censor some things. In a real war, we would not want to let the enemy know which of our units was going to be in a given place at a given time. This sort of censorship of information is vital to saving lives. Censoring information, however, is very different from censoring opinions. There is never any really good excuse for censoring opinions. If the government cannot keep the support of the people without resorting to suppression of opinions, it is in trouble. A democracy cannot stand for long if it is going to prevent people from disagreeing with its policies.
Thus, I would argue that there is no reason to curtail freedom of opinion during wartime. Some facts and information should be censored to save lives, but opinions should never be censored in a democratic society.