Why does one require proof of the existence of anything?
Most people structure their entire lives around a God not proved to exist.
Most people know that humans cannot flap their arms and fly safely from the top of the Empire State Building. Facts like that keep us alive.
Facts and proof are part of the fabric of our society, the reason why our laws are written and the basis of our entire system of mercantile commerce. Without proof, claims cannot be validated and without validation there exists no standards to which we may draw upon for truth.
Would you invest in companies or give out your credit card number over the phone without any proof of the caller's claims, or even proof that the company exists?
The reasons to require proof are far too numerous to name.
The countless millions of people who have lost their lives through murder, torture and as the result of terrorism, along with the countless trillions of dollars in property that have been destroyed are directly due to the lack of proof of diametrically opposing propositionally ideological philosophies.
Religions that believe they have the only path to God, the only book that has been authored by God, that certain geological locations have been given to them by God and that all those who do not believe must be either subjugated, converted or killed cannot exist within proximity to one another.
This has been a catalyst for local destruction for millennia, and now that we have what appears to be a portal from the fourteenth century open onto our world with inhabitants pouring through by the tens of thousands that have access to twenty-first century weapons puts it on a global scale of potential mass homicide.
Imagine all this NOT ever having existed if proof was required outside of ancient texts written by ignorant men with little or no understanding of the world, the universe and basic human physiology.
Yeah, we should demand proof - proof is, well, kind of important. It may even mean the difference between life continuing on this planet or our extinction.