If the past four years have taught us anything, is that just about every aspect of our government is ripe for fraud when the party in charge doesn't care about the well-being of the institutions they supposedly hold dear.
It seems like you're trying to make the case that we should listen to the man telling us mail-in votes are fraudulent... because his administration is exhibiting signs of committing said fraud?
For what its worth, we've been mail-in voting in Colorado for a while. Works great when the government isn't actively trying to undermine democracy.
This is about interference with the delivery the ballots (both from the election officials to voters and to vice versa), not about the security of the ballots themselves.