Good job you've been lucky. I'd say 9/10 times its fine. The issue is the 1 time it's not they have an absurd amount of power over you and can absolutely ruin your day over something petty.
Some agents absolutely take that exhaustion out on travelers.
And to your movie theater example same thing. The vast majority of times its fine, but once again I've had a few times where a group sat behind me that wanted to talk to each other and not watch the movie. It's annoying, but rare.
Did you consider the possibility that people complain about the times that are bad and not the times that are good?
Also you only addressed 1 point of my comment the attitude of TSA, not the systemic issues that make the system asinine