The media's a big help to terrorists, yes, though they are not "the only ones that can successfully manipulate the masses." They're a tool through which people hear of events. Much smaller scale and a little funny... at the office there's someone who... let's just say that from what the guy's say, this man needs a doctor/exorcist/nutritionist, not to mention a little help with how to use a modern toilet. He's been dubbed the toilet terrorist. Most of the guys now walk two buildings over to use another toilet, it's gotten so bad. Everyone walks past the men's room door (it's between our offices and the exit) holding their breath, for fear that the smells-so-bad-we-can-taste-it stench will be there, even when it's not. We learned of our "terrorist" a totally different way.
Yep, the media decides who should be "feared" and that's a big factor in modern "terrorism." Real terrorists, of course, know this and try their damnedest to use the media to their advantage.
Government policy and stories of corruption for instance, in my DEA example, are not really spread around directly by the media. People in immigrant communities get pretty scared of la Migra based off of stories they hear of being dragged off (legal or no) in the middle of the night. There's an awful lot of overlap in the world on this, and I know the way I define it is problematic. It's just the way I see it.