The video strongly implies that Muslims as a group are violent (watch the part with the father and daughter early on). It presents Islam's founder as a horrible human being, and a religious fraud.

This is not quite as mild as it gets with regard to criticism of religion, but it's pretty close. If this particular video were to be legally actionable, no criticism of a religion where it intersects with testable reality (making positive claims about nature contrary to science, claims of historical fact) would be safe without fear of prosecution. I am sorry that so many people have died, but I cannot blame this video without completely throwing out the American version of free speech. I guess we're just going have to solely blame the killers instead.