נהגו כבוד זה לזה means that those that there were “Litvish/Yeshivish” held that their way of Avodas Hashem was the ONLY way and PROPER way and BEST way, and were disparaging to other derochim in Avodas Hashem, including mocking the derech of Sefardim, Yekkas, Chadad, Satmar etc. In reply these groups of Talmidim made fun of the derech of “Litvish?Yeshivish”.
They all meant “l’shem shomayim” – coming from a good place, to “help” their fellow talmidim, after all, their Rebbe taught them that Ahavas Yisroel is a klal godal baTorah, and they REALLY had Ahavas Yisroel. They had good intentions, not merely to mock or put down (as many here do), they did so out of love and caring, yet, they were chayov misa.
Why such a harsh punishment for merely not treating an individual with proper kovod? Because they were knocking not just an individual (a yochid) but an entire derech of avodas Hashem. They were mocking hundreds or thousands of yidden – that deserves misa!
When a person knocks an entire derech of a kehillah which has rabbonim, rosh yeshivos, bnei Torah, even if one was to question how they do x or justification for y (like not sllep in sukkah, or eat cake before davening), it is a HUGE achrayus! Even if done out of love and care – the onesh is misa!
(Misa is manifested in many ways, loss of parnasa – poor is choshiv k`mes, loss of children – physically or spirtually etc)