>I mean some of these people are really smart and understand how this spying can be abused. There must be something they know that makes them build or support these programs.

just look at the recent 100 years of human history - good and smart people can perpetrate awful things if they suitably organized and informed. "Just doing my job", "just carrying out the orders", etc... In 21st century in the world's most progressive country, government employees and contractors were torturing other people just because some government lawyer wrote a memo saying it is a good thing.