[ivi0nk3y]

No, Nanami, I mean she is mentally unstable due to her parents murders. The fact that it happens while shes a kid more or less defines her character. This instability then causes her to be brain washed by Kira, even more, easily. Although she is willing for this to happen, when it happens because by that time she is infatuated with him.
The other people who cause riots and are apparent "followers" of Kira are actually condemned by Light himself to be nothing more than thugs and opportunists. i.e. the mobs attack on where they think the SPK (Nears' group) are residing.
As for the others within the Manga, you gotta bear in mind that it isn't the real world i'm talking about. Within the Manga, the people who all follow Kira have had some kindof pain of loss. They have seen bad things happen around the world and want justice. This is why they follow Kira. They just don't know who Kira is and what he is, so they call him a god for his god-like powers. It doesn't make them psychotic but I meant to call those thugs psychotic. It is those psychotic people or unstable people that Kira can manipulate so easily. If not because of his power, then because of his looks, charm and apparent status.