From Slate's "Dear Prudence:"

Dear Prudence,
My son is 21, a junior in college, and seriously dating an 18-year-old freshman. He brought her to our house for Thanksgiving, and she is attractive and charming. The problem is that we are Jewish and have mandated to our three sons that they must marry a Jewish woman. We are heartbroken that he is dating a non-Jewish woman. We are not sure if we should forbid him from dating her or if we should leave them alone and hope that they break up and he finds a nice Jewish woman to marry. Please don't tell me that I should get over this and accept whoever he wants to marry. My wife and I cannot accept a daughter-in-law of a different faith. I don't want to over- or underreact, and don't know what to do.
—Heartbroken

Dear Heartbroken,
How's that going to work, your mandating that they marry Jewish women—will they be banished from the shtetl if they don't? You must secretly want gentile daughters-in-law, because if you continue with your current approach (how do you forbid a grown man from dating someone?), you are on track to get three. Since you are observant Jews, perhaps you've run across an account of the temptation of forbidden fruit? Constant harangues about non-Jewish women will only increase their allure. I truly understand your desire to have your sons marry Jews and raise Jewish children. Surely over the years, you have expressed to them in positive terms the joys of having a Jewish family and your hopes about Jewish continuity. Now, the best thing you can do is make your home as appealing as possible. And if any of your sons decide to marry non-Jews, your best chance for having these women embrace Judaism is to be embraced by their loving, Jewish family.
—Prudie

(Discuss amongst yourselves.)