“Fire in a theatre” is a great example of using a reasonable sounding analogy to support behaviour (prosecuting anti-war campaigners) that today we judge very poorly.
Not to mention even in light of the historical context, one should strongly support the free speech rights of anti-war protestors, but inciting panic in a crowded space ('fire' in a crowded theater) isn't the correct way to go about it.
I think it stands as a good example of how restrictions on certain kinds of speech that look very reasonable in a moment of crisis can in turn be judged very poorly in the long term.
I don't personally know where I stand on the free speech issue, I just want people to stop using this stupid "fire in a crowded theatre" analogy.