Cliffy, there are two kinds of realities. What you are talking of are metaphysical realities. Thus is the world a good place or a bad place, is contraception good or bad, is Keynesian economics more realistic or is supply side economics, these are metaphysical realties. And here you are right; you will find evidence depending upon your point of view. Whatever your preconceived point of view, you will find evidence in support of that.
However, then there are physical realities. They do not depend upon our subjective thoughts (not in day to day world anyway, they do when one approaches relativistic conditions, when one approaches the speed of light). These are absolute realties, and a person denies them at his own peril.
Thus if you deny the reality of gravitation, and walk off a ten storey building, you are the only one who will get hurt (well, unless you land on somebody else). Or as Gilbert said, you may think a rock is as soft as cotton, but it still will smash a window to pieces.
So it is important to distinguish between metaphysical and physical realities.