In cases like this, I would aim to be extra careful to make a kiddush hashem, rather than the other way around
I am SO with you, on this one! Of course there is the fear that by having cordial relationships with non-Jews, it will CH”V lead to intermarriage. That surely is a legitimate point. But the enmity that erupts when a Jew interacts in a dishonest or nasty way with a non-Jew, can do more damage than anything. Wherever we live, we live with the tolerance of the non-Jewish world. Perhaps we don’t like to think that, but historically it has always been true. we lived in every society, building their economy up, under their sufferance, until Hashem decided, “genug,” and we were A) exiled, b)murdered, or c)enslaved. It would be so wonderful to not have to worry about our relations with the nochri, but the fact is we are not in our own land, and we are only safe here for as long as Hashem deems it so. And so, as with Herr Rabiner, it is not a bad thing to always act with menschlechkeit to ALL people.