Because three hundred years ago, while Zhen Chu was out training with his favorite disciple, they happened to encounter the Demon Sect. Several Hall Masters from the Demon Sect blocked Zhen Chu, and then another Hall Master killed Zhen Chu's disciple, brutally harming him in front of Zhen Chu, which is why Zhen Chu has such great resentment toward the Demon Sect.
For the Demon Sect, Zhen Chu wishes they were all dead. This is very normal, after all, back then there wasn't this organization, and the righteous path and Demon Sect were mortal enemies. When they met, it was either you die or I perish. So this kind of slaughter was very normal, but the hatred gradually built up like this. Moreover, as long as there is slaughter, there will be hatred, unless everyone is killed, which is impractical. To make the hatred from Zhen Chu's side disappear, the entire Taichu Sect must be exterminated for their hatred to vanish, otherwise it won't.
