Yes, undoubtedly there are good candidates who are weeded out due to false positives, but there are probably many bad candidates who are weeded out due to true positives (or don't apply at all because they fear the test). It will lead to bad actors who study the test and pass it, but that's why it's critical that law enforcement agencies do not use a passed test as indication of trustworthiness; merely an initial barrier to entry to be passed. The trustworthiness has to come from a thorough background check and normal interviewing.

As long as the examiners, recruiters, interviewers, and higher-ups fully understand polygraphs are a trick and nothing more, I still think they serve a useful purpose for three-letter agency hiring.