You're mistaking sex for love/trust. Sex is a physiological function that provides physical pleasure and is instrumental in procreation. Love and relationships provide emotional well-being, a partner in financial and materialistic endeavors, and a support system for the roller coaster we call life. If an open sexual relationship is wrong for you, that means that it's wrong for YOU. It can (and often is the answer for others, and you don't get to condemn them for that. Open your mind.