As you say, they could accomplish the same thing by checking IDs at the door. Given the choice, I'd personally prefer an explicit ID check that I know is happening and is inconvenient for everybody rather than one that leaves me oblivious to the fact I'm being tracked and researched.
As you say, they could accomplish the same thing by checking IDs at the door. Given the choice, I'd personally prefer an explicit ID check that I know is happening and is inconvenient for everybody rather than one that leaves me oblivious to the fact I'm being tracked and researched.