my guess is that he was trying to weaken a bit Yoshiki's undisputable and self-centered leadership by asking him to accept all the members' inputs in composing songs (also, I think he made a point about everybody being treated equally from an economic standpoint). Basically he wanted a bit of democracy in the band, imo. He definitely didn't want X to be a monarchy, rather a shared project.
however Taiji never made a mystery about the fact that Yoshiki is "both an angel and a devil", these words are taken verbatim from his autobiography.
another guess is that there were drug related or drinking problems. I bet that Yoshiki was willing to put his life on the line to keep X as clean as possible in order to think through carefully about their debut in the U.S. at the time.