We should actively encourage them, as Rabbi Chaim did, for we can learn from their observations, eliminate our character defects, and thereby better ourselves.
Judaism presents seven mitzvot for non-Jews to observe.
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As explained in the Talmud (Sanhedrin 58b), they include the prohibition against theft, murder, and sexual immorality.
These are the pillars of human civilization, and are named the "Seven Laws of Noah," since all humans are descended from Noah.
As you could imagine, this would create a variety of confusions regarding the person's religious identity, and that of their children.