Since I already expect to be seen, one more person looking at me isn't a big deal. My public appearance is public, but my private things in my bag are not. It's incredibly uncomfortable (and IMO demeaning) to have someone examining the extra pair of underwear in your gym bag or skimming through your journal looking for proprietary info.
They would (presumably) not be allowed to read a journal for the purpose of theft detection. And if you would be made uncomfortable by something you brought to work, and it wasn't required for your job, you could leave it in a vehicle or at home. Sure, being able to bring it into work might be a personal convenience, for example if you take public transport and wanted to go to the gym before, during, or after work - but it's a choice. It isn't possible to opt out of surveillance.
That’s how it is random. It’s milder because you get in trouble only if you have something in your bag that’s not supposed to be there and since it’s random you don’t feel targeted.