Logical Fallacies

For about a year now I've been considering the idea of posting a weekly logical fallacy. At first I thought it would just be boring. However some recent events have caused me to realize that the world could use another lesson or two on how logic really works compared to how people think it works.

Circular reasoning
A couple of friends of mine and I were curious as to why so many fleet vehicles are painted white. I speculated that since white paint reflects more light then white cars wouldn't get as hot. A friend of mine countered by claiming that white paint is cheaper. So I asked, "Is white paint really cheaper?" His response, "Of course it is, why else would there be so many white cars out there?" I've never before had such an obvious case of circular reasoning presented to me as if it was logic. In his mind white cars are more abundant because the paint is cheaper and his evidence that the paint is cheaper is because white cars are more abundant. The car's color is proof of cheap paint and cheap paint is proof of the car's color.
In my suggestion I started with an established scientific fact; the color white reflects more light than other colors. Therefore, a white car would not absorb as much heat as a green car.
Granted this is a relatively trivial water cooler conversation but I've seen the same illogic used in much more serious issues. I am all for debating controversial issues. I just think that our justifications should be based on logic and not circular reasoning.