Chemical detection doesn't even get used except under "random" search. There are so many chemicals to test for, and so many of them have other common uses that

Chemical detection doesn't even get used except under "random" search. There are so many chemicals to test for, and so many of them have other common uses that using chemical tests as a proxy for malicious intent has poor accuracy. Even assuming tests are extremely accurate, false positive rates would still massively exceed the incidence of threats. What you look like will greatly increase your odds of being "randomly" searched and thereby odds of false positive chemical detection, at which point what you believe may become a liability during your interrogation. Having an objective mechanism in the mix doesn't really put a dent how culturally and racially biased the present solution is. Whether you feel a need for there to be such a system in place only changes whether such a bias is a matter of xenophobic overreach or a technical weakness against threats that resemble the majority.