I would argue that a democratic government should be very wary about ever curtailing freedom of speech. Freedom of speech is necessary in order to have a liberal democracy and we do not want to endanger it.
Of course, wartime is a special case. However, even then, we should only curtail freedom of speech that is directly harmful to the war effort. That is, we should only curtail speech that would directly help the enemy. This would include revealing war plans or troop movements or tactics.
We should not curtail speech that simply tends to be anti-war. We have done that in the past (notably in WWI) and it is not good for our democracy. If we go to war, our reasons should be good enough to withstand criticism in the public arena.