Assuming greed is evil, as you stated, one evil is not greater than the other, but one greed can do more good than the other. Greed in a competive business world can be a good thing, and greed in a democratic political system can be a good thing. Note I use 'can' and not is.
You assumed that that people who own businesses are good at them, and that politicans have no idea how to run a business. This is not true. For instance, what if the water company owner had no idea how to run a business and merely inherited it from someone else? He would not be qualified to run the business. He could hire other people else to run the business, but he still wants to make a lot of money for himself, cutting into efficiency.
Not all monopolies are that way because of a business 'being too good at what it does.' Many monopolies are regional monopolies (like the water company) and it is not viable for competition to occur. Take the water company for example, you have one pipe running to your house and one system running through your city. Could you imagine what a nighmare it would be, or how inefficient it would be, to have 2 or 3 water companies with their own pipes going all over a city?
