The difficulty is of course, that if everyone complied with this, then the queues may get smaller, but guess what..they'd then cut the numbers of security personnel, and the quesues would get bigger again. It's about maximising profit, not providing a good service.
When passing through security, I simply refuse to be barked at by some moron wearing a yellow vest. I ignore these goons when they are shouting.
The last time I went through Gatwick, security was a friggin joke, with queues outside the building, and lots of nobs strutting about shouting to people telling them where to stand etc..
Do not let these people harras you into thinking you must move quickly or get stressed, just take your time, and stay really unstressed by the whole experience. If other people or staff get stressed, then that's their problem.
If there are delays it is down to incompetent management, not the travelling public. Never forget, you pay for the security checks in your ticket, and deserve to be treated with respect.