Why a number of sociologists believe that ethical violations occurred in Laud Humphrey's study of "tearooms"?

In “Tearoom” Trade “Laud Humphreys” expounds on the gay person relations that occurred in different “tearooms” in an unidentified “American” city amid the mid-to-late 1960s. By professing to be a basic voyeur “Humphreys” clarifies that he efficiently watched these exercises and even recorded the tag quantities of a specimen of “tearoom” members. Why a number of sociologists believe that ethical violations occurred in Laud Humphrey’s study of “tearooms”?