"For argument's sake, let's postulate that natural selection is completely wrong, that some other non-supernatural, purely physical or chemical mechanism creates the changing diversity of the biological world. "

Like for instance, radiation?

"And let us assume that we succeed in proving it by methods acceptable to science, and that scientists are convinced by these proofs. Darwinism is discredited and a new theory takes over. Don't laugh,"

Good idea.

"...this sort of paradigm shift happens frequently in science! The creationist/IDers would not accept this new theory either, regardless of the evidence available for it. They are not trying to disprove Darwin, they are trying to preserve Genesis. They can never be satisfied, regardless of the evidence, and that is not science. You simply cannot reason with these people."

I agree completely.