First off in other countries you don't have a "middle class" that might travel occasionally, but not regularly enough to keep up with the rules.

In other countries ALL WORKERS are expected to be treated with respect. In the USA the norm seems to be to beat up on any worker deemed less respectable than you. I was yelled at by my Australian wife because I didn't say Please TWICE when ordering something from a menu. My usual statement is "can I please have burger." She told me I was expected to say please at the beginning AND end of an order in Australia. Now that my friend is RESPECT.
TSA employees get so much disrespect that its just natural for some of it to flow back at the passengers. It might not be right, but its the way it is.