The correct answer to this open question is the following.
I think the United States federal government always has to allow people to express their opinions, no matter if the country is fighting a war. Americans should permit political dissent in wartime as long as the criticism is respectful, and never compromises the strategy and tactics of the United States military.
The fact that people could express their opinions -even during wartime- really confirms the democratic commitment of the government and the respect for the freedom of speech right stated in the Constitution.
People can support or question the motives of US involvement in a war. A mature society like the United States should accept that.