The proof is short- three words really: the modern era.

If fundamentalism succeeded, the modern era would not have re-shaped every culture on earth. Really, you could shorten the proof even further: progress. All cultures progress, change, reshape themselves and their values over time, and thus fundamentalism always falls before newness.

Even logic/reason defies itself as a fundamentalist philosophy- You can use logic to decisively prove that there are things you can not prove. And even that truth yields to reasoned estimation of semantic value (the really very probably true and the almost certainly false).

Heraclitus had it pegged before there even was any rigor to philosophy or math. The world is fire. The human realm is to noisy to live by fixed immutable 'basic' principles. Humans crave the simple appeal of fundamentalism like a dog craves a bone- but the point of intellect is to rise above base drives. BooHoo, the world is messy and won;'t bow to your fundamentalist principles. You can either grow up, grow a brain, and adjust/innovate/learn- or you can purge the impurities and the impure in the hopes that god will like you again, or that your first principles are simple and elegant enough to flourish again... In which case, history has a dustbin full of dead philosophies and religions just waiting for you.

Fundamentalism is the first failed philosophy, and one that refuses to go away.

Yeti