It’s true that an antigen test (that tests for the virus itself) would be better than an antibody test (that tests for an immune response to the virus), other things being equal. But given the exponential rate of increase in new infections right now, most of the people who test positive on an antibody test right now will turn out to be currently infected, not recovered.
The point of the test is not to classify people as vulnerable or not vulnerable to infection. The point is to use the test to trace contacts and isolate the infected. Those who test negative should still be using social distancing for the duration. Those who test positive should be isolated, and then after a period of quarantine, return to social distancing for the duration like everybody else. No test result should make anyone think they are “safe” and allowed to return to normal.
