B’’H Shalom, I recently read a reply by one of the rabbis concerning those who wear black kippot and why they are typically less likely to return a greeting, even the yeshiva students, as opposed to Jews who wear knit kippot who are friendlier and always eager to help. The reply did not satisfy me, since I have read in Talmud Berachot 6b by Rabbi Chelbo in the name of Rav Huna that if a person greets the other, and the one greeted does not reply, he is called a robber. Now, how can such religious people violate such a miztvah? I believe reference was made even to yeshiva students who definitely know of what the Talmud says. Are there any other teachings or rulings concerning this matter?
Generalizations are dangerous and from my experience there are those who will greet you or return greetings from all sectors of society. Perhaps what you heard is that there are groups who see the unity of the Jewish People - including those who are presently non-observant - as important and who encourage social contact with all groups, while there are others, who may also believe in the unity of the Jewish People but who fear that social contact with the non-religious may cause harm. Here too, it would not be at all correct to say all those who wear black hats belong to the second group.