Highsmith was a resolute atheist. Although she considered herself a liberal, and in her school years had got along with Black students, in later years she became convinced that Blacks were responsible for the welfare crisis in America. She disliked Koreans because "they ate dogs".
Highsmith was an active supporter of Palestinian rights, a stance which, according to Carol screenwriter Phyllis Nagy, "often teetered into outright antisemitism." When she was living in Switzerland in the 1980s, she used nearly 40 aliases when writing to various government bodies and newspapers deploring the state of Israel and the "influence" of the Jews. Nevertheless, many of the women she became romantically involved with as well as friends she valued were Jewish, such as Arthur Koestler, whom she met in October 1950 and with whom she had an unsuccessful affair designed to hide her homosexuality, believing that Marc Brandel's disclosure that she was homosexual would hurt her professionally. Moreover, Saul Bellow, also Jewish, was a favorite author.