The pat downs are sexual in nature because they are done by rubbing the palms against the persons body including the genitals and breasts on women.

A police officer conducts this type of pat-down when a person is arrested or is in the process of being arrested or detained because there is a sufficient threat indicator. What the TSA is doing is saying that either you get irradiated and people get to see you naked, or you're a potential terrorist/criminal.