@RSo
“There is no inyan of arvus in encouraging goyim to keep their mitzvos. ”
רמב”ם הל’ מלכים פ”ח
וְכֵן צִוָּה משֶׁה רַבֵּנוּ מִפִּי הַגְּבוּרָה לָכֹף אֶת כָּל בָּאֵי הָעוֹלָם לְקַבֵּל מִצְוֹת שֶׁנִּצְטַוּוּ בְּנֵי נֹחַ
The Rebbe based his campaign on this Rambam. Yes, obviously, there are different opinion and there are those who disagree with the Rebbe. But to call ‘stam mishigass’ (instead of perhaps ‘a minority opinion or the like) shows a lack of knowledge on your part.
P.S. The Rebbe did not want it done with cards and the like. There are letters (or more accurately מענות) of the Rebbe to that effect. Additionally, I am almost positive that it was not meant for bochurim but rather those who have contact with non-Jews either way