Sforno on Leviticus 18:30/ספורנו על ויקרא י״ח:ל׳

1ושמרתם את משמרתי לבלתי עשות מחקות התועבות, observe also the legislation which is in the nature of a protective fence against the major sin of indulging in actual sexual relations with the forbidden partners. Just as the legislation governing menstrual laws, eating of forbidden foods, sleeping with a woman ritually impure after giving birth, etc., have all been surrounded with what our sages call a סיג, “protective fence,” this legislation too has such a protective fence which must not be ignored except at your peril. The overriding consideration is לא תטמאו בהם, “do not become spiritually contaminated by ignoring these laws.”