Proof by belief creates truth vacuously. Proof by fact defines truth incompletely, yet provides a consistent frame to expand understanding. Where theory crosses into fact may be a function only of one's desire or ability to comprehend accumulating fact.

It's effectively impossible to prove the scientific rational to those who entertain only belief, and those who substitute belief for fact do so at their (and unfortunately others) peril. The deeper more interesting question is, "Why do they do so?"

Substitute the word "gravity" for "evolution" during creationist arguments. What do you conclude? Those who wish to explore divine intervention should post to philosophy or religion, and leave science alone.