The current patents under the Monsanto Company provides them with unfair economic control over the farmers who buy and grow their crops. Patenting living, biological organisms creates unnecessary and complicated problems of regulation of the patent, revoking patents that provide a company or individual ownership solves most if not all of these problems.
As it stands, the most Monsanto and similar companies gain from harassing farmers, who use their products to the best and fullest extent, is to create a monopoly against them to create an unsustainable profit by racking up prices afterwards.
As an additional fail safe to prevent this from happening in other markets, it should be impossible to create patents of other natural or manufactured organisms as well as the byproducts they produce.