Do you disapprove when a forum mod bans a troll? What's the difference? It's a matter of good or bad faith. If you don't discourage bad faith behavior, then everything gets torn apart in the name of freedom. This is the anarchist saying this. Like everything else, free speech is not a pure black & white issue.
Forums are private areas of the internet. Moderators can ban people to keep the forums how they like them to be, and users will move towards a forum with an atmosphere they like. If someone is banned from a forum that doesn't mean they can't still say what they were saying - it just means they have to take it somewhere else. Arresting people for "trolling" in real life would be completely different.
I do think there are some limits on free speech, but to be honest I don't think this film breached any of them (there may be contractual issues with the actors but that's another matter). The ones I can think of are:
- Serious slander: spreading lies about someone to damage their reputation
- Harrassment: going after a specific person or people and undue grief (this one would take a while to properly define, but I think you can see what I'm getting at)
- Inciting violence: telling people to commit acts of violence, especially people who you have a degree of control over
- Hoaxes that inconvenience others or cost a lot: stuff like yelling fire in a crowded theatre
I don't think criticising a historical figure or a belief system really falls under any of those. In any case the embassy attacks were almost certainly planned ahead of time and more as revenge for the assassinations of high up members of al-Qaeda than for some film that almost noone watched.