“Rav Chaim of Volozhim was the prime student of the Gra, yet he did not sign the Cherem against chassidim! The LItvish of today follow the ways of Reb Chaim, yet the haters keep bringing up the Gra’s cherem (that Reb Chaim had no part of”
Rav Chaim Volozhin was a Misnaged. The Chasidim try to make up and sell a bobbeh mayseh in which Rav Chaim Volozhin differed with the GRA and refused to sign the cheirem, based on the fact that his signature is not on it. As if he was not a Misnaged.
So why didn’t Rav Chaim Volozhin sign it?
A few reasons are given, see sefer Hagaon by Rav Dov Eliach shlita.
For example,
1) The cheirem was put out by large kehillos, such as Vilna, Brisk….R. Chaim was in a small rural town, Volozhin, so he was not part of it. It wasn’t like a heter meah rabbonim, when people might go around to get signatures from all over. Also, in the old days travel and communication were much more difficult than they are today.
2) R. Chaim Volozhin didn’t want to sign along with his Rebbe, that could be seen as disrespectful, as if he was on par with him.
Later on, the government of Czarist Russia legalized Hasidism, so the cheirem could not be enforced.