It strikes me that non-halachic "pegam" has a long history in that we can even read it into the story of Ruth the Moabitess. As the pasuk states in Ruth 4:
lest I mar my heritage my offspring, like (Ps. 127:3): “Behold the heritage of the Lord is sons,” to give my offspring a stigma, as it is said (Deut. 23: 4): “An Ammonite or a Moabite shall not enter the congregation of the Lord,” but he erred by [not interpreting it as] “an Ammonite but not an Ammonitess.”Rashi thus interprets this as a assuming that this is an halachic error. We may further interpret this as knowledge of this halachic conclusion but adopting the stringent non-halachic position anyway because, when it comes to pegam, people do that.
Update: Just to clarify, I know many people who have absolutely no problem dating and marrying baalei teshuva because of a problem of "ben-nidda-ism." But just as surely, I have heard of/encountered people who will not.