Several people (among them Chris Hanson pointed at The Basic Laws of Human Stupidity, written by Carlo M. Cipolla:

The first basic law of human stupidity asserts without ambiguity that:

Always and inevitably everyone underestimates the number of stupid individuals in circulation.

…I firmly believe that stupidity is an indiscriminate privilege of all human groups and is uniformly distributed according to a constant proportion. This fact is scientifically expressed by the Second Basic Law which states that

The probability that a certain person be stupid is independent of any other characteristic of that person.

…As the Third Basic Law explicitly clarifies:

A stupid person is a person who causes losses to another person or to a group of persons while himself deriving no gain and even possibly incurring losses.

When confronted for the first time with the Third Basic Law, rational people instinctively react with feelings of skepticism and incredulity. The fact is that reasonable people have difficulty in conceiving and understanding unreasonable behaviour…

There’s much more to it, including lots of stuff on the main True Stupidity site. All, sadly, true.