Because they are hippies who fear an alternative energy that might actually work, and they listen to horror stories about things like Chernobyl and Three-Mile Island, ignoring that fact that neither of those are possible with a well-designed, safely implemented reactor. Things like a nuclear plant going critical is only possible if the plant was designed by a drunken idiot, and staffed by retarded turtles; neither of those is the case with the reactors in Japan, which are fine.
And they get scared by radiation, because they can't understand it, even though you get hit by more radiation watching TV than you do walking around a nuclear power plant.
EDIT: A friend posted this article on Facebook, makes sense to me.
http://theenergycollective.com/barrybrook/53461/fukushima-nuclear-accident-simple-and-accurate-explanation