This really is a divsive issue and is one that has valid arguments on both sides. On one side there is the argument that it is in the public interest to broadcast these message so that the public know the threat they face. And on the other side there is the argument that it gives the terrorists attention, a political broadcast and an opportunity to spread their message of hate and lies.
My Personal Opinion: Whether these videos are shown should remain at the discretion of the channel in question, but the channels shoudl give serious consideration as to the content and audience of the film. Most of the video's should not be shown as it in effect gives the terrorist a political broadcast to attract new extremists and sympathisers?