Why do the TSA enhanced pat down procedures not violate illegal search laws?

TSA enhanced pat-down procedures do not violate illegal search laws because individuals are not required to submit to them. Forewarned, pengers may chose another form of transportation if they do not want to comply with procedures. Those attacking the TSA will screech loudest when the next "underwear bomber" is successful. I wonder if they would change their mind if it were their plane.