Sadly, we have to fight within the system we have. The GAO points out the issues (including lack of empirical data that SPOT works), it is up to us to push the issue.

Instead of saying "I don't think SPOT works" you can say "The GAO reported 'key individuals allegedly involved in six terrorist plots that have been uncovered by law enforcement agencies. ...at least 16 of the individuals allegedly involved in these plots moved through 8 different airports where the SPOT program had been implemented. Six of the 8 airports were among the 10 highest-risk airports, as rated by TSA in its Current Airport Threat Assessment. In total, these individuals moved through SPOT airports on at least 23 different occasions.'"

This is empirical evidence supporting the ineffectiveness of the SPOT program, not an opinion.