Elaborate on terrorist goals concerning media. With regard to terrorist goals concerning the media, explain how terrorists use the following to help their crusade: publicity, favorable understanding of their cause, legitimacy and identity, destabilization of the enemy, and media as a weapon.
Terrorists use media of various sorts quite extensively, particularly in this age in which social media are so prevalent. Looking at the topics you are considering, we can see how this is so.
Let us start by looking at your second topic. Terrorist groups are usually fighting against some condition that is not universally condemned. That is, there are many people (probably even a majority of people) who do not think that the condition is a problem. Therefore, the group is trying to achieve favorable understanding of their cause. To do this, the group needs to use the media to spread its interpretation of the conflict to its target audience. It needs to try to persuade people to see things in its way. For example, Al Qaeda needs to persuade other Muslims around the world that the West hates Muslims and is trying to destroy the Muslim world.
This connects to your third topic. A group has legitimacy if people believe that it is right for that group to act as it does. It has an identity if people perceive that the group exists and that it is important. Both of these things can be achieved through the media. Terrorists can use the media to establish their importance by doing things like claiming responsibility for attacks. They can use the media to try to establish their legitimacy by persuading target audiences that their ends and their means are just.
Your fourth topic is harder to achieve. In order to do this, the terrorists would have to sow a great deal of fear and confusion among their enemies. It is hard to do this through the media unless the terrorists have proven that they can back up their threats with specific actions. The actions are much more effective in destabilizing the enemy than any media tactics.
This brings us to your first and last topics, which properly belong together. The media is a weapon because it allows terrorists to garner publicity. It is a weapon because it allows them to disseminate their message and possibly gain followers and legitimacy. This is why terrorists are eager to use media of various sorts.