This is inverting the burden of proof in a very seriously erroneous way.
Say for example I assert, there is a ghost on the upper shelf of my closet. Does that mean we should all assume that is true until you prove it is false?
Fairly clearly not. That is what is meant by the burden of proof is on he who asserts existence. In this example, me because I asserted that there was such a ghost.
Applied to this case. The assertion that there has been widespread systematic voter fraud is an assertion that a specific type of fraud has occurred. Lacking at least plausible proof that this is the case, it is reasonable to assume it has not.
But another way to consider this is in terms of non-falsifiable beliefs. What evidence, which could exist in principle, would you find persuasive that no such fraud has occurred?
If one can't name any, then it is a non-falsifiable belief. These have all sorts of logical problems.
Finally, there is the more scientific way to consider the evidence and that is to objectively consider the evidence both for and against the proposition. What sort of evidence is there that coordinated systematic fraud occurred in the 2020 presidential election? I have been asking for some months now for an objective overview of the evidence on both sides and have not heard of one. The film "2000 Mules" was said to be worth considering in this regard. In my view it fails to present even a plausible case to back up its assertion to the effect. But I remain very interested in such an objective overview if one exists.
You, like so many before you, are confusing evidence with accusations. There is no evidence of a ghost in your closet beyond your assertion. While I don’t believe it, I hold out the possibility that with evidence, it could be proven, or at least support be shown to warrant a serious investigation.
That’s what we have here. There were initially accusations of fraud - expected, but a big nothing. Then there is data showing irregularities in voting patterns, patterns that are know to coincide with ballot box stuffing - Cobb county seeing a 40% rise in Democrats voting for example, more than voted for Obama in a largely black district. Beyond that, there is now video evidence of people dropping a dozen or more ballots at once into boxes and taking precautions not to leave dna evidence behind. There is forensic evidence of travel patterns which branch out from concentrated points and move to multiple ballot drop box locations.
These move into the realm of evidence of fraud and require deeper investigation, both because of the scientific nature of the evidence and the impact of what it means if true. Your vote and the vote of everyone in your family might have been invalidated by a mule.
Beyond that - many Republican are sure this happened and, given the Left’s gaslighting, believe their only recourse is to cheat in kind. It is critical to the integrity of elections that the truth be known. Otherwise, every election becomes tainted with a claim of illegitimacy.