Even armed with statistics or a report from a "legitmate" (paid) research firm, in the end you can always find something credible looking to back up what you say or believe. Often being confronted with proof to the contrary makes a believer even more convinced of their belief.
The real problem here is the difference between what people think, what people say and what people do. Everyone hates the screening process, and even the most law-and-order "nothing to fear if you have nothing to hide" Ward Cleaver type is going to see patronizing, questionable and occasionally abusive behaviour.
It can be scary to confront the idea that the government might not have your best interests at heart, and scared people are not likely to speak up unless something is happening to them.
People are herded like animals through the screening process. The entire scenario is designed to scare people into complacency and obedience. Herds are not known for thinking rationally.
In the end, there's no obvious way to get enough people in a herd to speak up. That means that people who do get frustrated and push back look like trouble makers, they are made to look like the suspicious ones. Anyone who might want to help is fighting against the fear that they too will be singled out.
It's a vicious circle experienced by anyone that flies frequently. Asking for "evidence" that people aren't upset is missing the point.