[Conspiracy theories sell in low income low IQ venues.]
Conspiracy theories sell when people are afraid.
In many cases that fear is reasonable, such as when there is a war or a depression or other disaster, but in this case the fear has been deliberately perpetuated by the Left for political gain.
Fortunately, I think that has a lot to do with it. At least where it actually may exist in the community. It does little good to remind people that they lived below sea level (I live in So Cal - visited at times by earthquakes, on the coast & in a flood plain, where they've pumped oil for generations and now pump seawater...): (*)
NO one actually believes it will happen while they are there to experience it.
When this stuff hits the fan people will grab at any reason that seems to take the uncertainly away - gods, racists, enemies, big business, whatever.
There are certainly other factors as well:
Urban legends of intentionally blown levees.
The whole OJ thing.
Class and race based expectations of governments' obligations to them.
Giving it all just enough legitimacy, politicians and the special interest blocs that live of off a fragmented society (JJ, Rev Al, Clinton/Carter, etc).
And, finally, yes, there are white racists in society, just enough to give some credence to all of the above; just as there black racists ready to take advantage of it.