Because they are democratic institutions. They can be held to a no-problems standard because every time a problem occurs then those involved can be sacked and replaced. The level of acceptable corruption is set by the membership. Rules should therefore focus on openness and member participation in leadership selection. Everyone who hates unions because of X or Y, to them I say join the leadership and run the union the way you think it should be run. Tearing down the system doesn't fix anything.
