I make the background black, because contrary to your assertion, it IS easier to read and MUCH easier on the eyes. Stars in the night sky is the best analogy.

White backgrounds cause pupils to contract which makes vision less effective (unless you're very long-sighted or presbyopic, perhaps).
Too much backgroud light puts undue strain on the retina and optic nerve.
Haven't you heard of snow-blindness? It's the same effect and it ruins the eyesight of IT workers.
You're interested in the text, not the background, so why flood your retina with background light?
Monitors also emit much more UV radiation with white backgrounds, though admittedly that was more of a CRT problem.