Yes because the same amount of Americans would have no problem bombing "dem towelheads" if the people there acted like decent human beings, right? Propaganda, even the crudest form of it, must be fed with something and the guys there do an excellent job fueling it almost by themselves.
Because you know what? I consider myself a pacifist person but even I would probably feel not too sorry if a random sandperson got killed after they burn my flag twice a day.
Also, just so you know, what people think matters even if places like Iran. Propaganda exists for a reason because, in the end of the day, if nobody supports a regime it will collapse in a day.
Edit:
Which one do you think will change american policy more:
One letter to Obama where people very kindly ask him to leave their nation and let them be in peace, or thousands of people marching in Kabul shouting Death to America, burning their flags and attacking any US troops there?
If every single one of then wrote a single letter, asking the US to leave and stopped blowing themselves up, the US troops would leave by the end of the month. Do you really doubt that? Now, the influence would remain, sure, but the various countries could actually start having a functional country.