Saying "I would do X when presented with Y" is easy to say when you have not been presented with Y. Regarding the wallpaper, yes, it's inappropriate. Perhaps it is an indication that the people are drunk with power. But it could also be another instance of people in an uncomfortable situation using humor as a coping mechanism.
In The Gift of Fear, Gavin de Becker talks about how, as a security consultant, he takes offhand jokes very seriously. He tells the story about the office which received an odd-looking package that nobody was expecting. They debated whether to open it. Eventually one guy decided to open it, so his coworker left the room. As the coworker was leaving, he made an offhand joke over his shoulder: "I'm going to stand in the other room so I won't be around when the bomb goes off."
Then the bomb went off.
Jokes are designed as a mechanism for saying speculative, potentially scary things without being threatening or looking stupid. When I see a TSA agent with that wallpaper, I see someone who knows at some level that something is very wrong but isn't able to say so out loud. Maybe they can't even say it out loud to themselves.
You mean, so uncomfortable that you set your wallpaper to a funny picture? You're right, clearly anyone that uncomfortable couldn't possibly be doing their job well.
It's pretty tasteless, but give me a break. Some guy is "drunk with power" because he thinks an image macro is funny?
I don't think cops breaking the law is analogous to people making inappropriate jokes about their work to colleagues. There are valid ways to argue against these machines and the policy. I do not think your line of argument is one of them.
