If they are running a temperature they must go home, right? That's a red light test. You are correct though, temperature readings are terrible green light tests; worse than LFD's.
It's bigtime apples and oranges. A temperature check isn't a green light to stop social distancing. A assurance green light is. A temperature check isn't an assurance of non-infected. An assurance green light it.
This is as apples and oranges as it gets. False negatives kill people.