It's intended to be stressful because that gets people to crack. My advice is to not take it personally unless they really push the line. The stress is part of their procedure to make sure you are not lying.
However, for someone with a gun on their belt, having got their education from Hollywood films and with a government that snitches on the world to lock up dark skinned people in Guantanamo I guess this jobsworth mentality makes sense to them.
Upsetting people who have good money to spend means they don't come back. You don't want to be treated like garbage by imbeciles that insult your intelligence. It is taken personally. The U.S.A. is not that special, it is just full of entitled people that think they are special.
There is no reason they cant do the same job while treating everyone with respect. When you work with a group of people that see themselves as hammers, everyone else is a nail.