“Another flaw they point out is that historically Easter has been worse for the Jews than any other holiday, yet no such minhag exists on Easter.”
After the supposed yartzeit, apparently they wanted revenge. One can make a chiluk between the two as to why no such minhag came about for Easter. The solstice holiday was one night where small bands of drunken peasants were running around. For the other, it could be that a small army was tearing through the countryside. There was no way to hide. Life had to go on.
Anyway, enough of my conjecture. yitayningwut, do you have a theory as to what’s the origin of nittel naght?