What do you think about banks?

They are useful institutions.

I think they are an absolute necessity to keep rivers and creeks from spreading all over the land.

When other people have access to your money, and the power to cut off the flow, you are at their mercy. However, if robbers knew that there was not any banks, and all people kept their money in their homes... there would be a stronger increase in home robberies, and no doubt, those who have money will invest in even stronger defense systems surrounding their homes.