Unfortunately, you can never prove or disprove the negative. The TSA will claim that since there have been no major incidents since their draconian security program has been instituted, their program has been 100% effective. However, than can not or will not tell us of any hijack attempts that they have blocked so there is no evidence to back up any of their claim.
There is, however, ample evidence to show that they have made air travel even worse than it was. There is ample evidence that the people who paw through our luggage steal from our luggage. There is ample evidence that some of the TSA people enjoy being in a position of power and enjoy humiliating people. There is ample evidence that TSA people make insulting remarks to people.
Are we better off with them. Probably not. Is there an alternative to them - I am not sure.
DON