I agree with flyingfox 2002 that it is a problem of intrinsic violent nature of Kau Cheen Yan that caused him the problems in ROCH. Indeed, it is unbelievable that a person who has spent over 20 years to learn Dharma and Buddhist philosophy still has such feeling. In any events, I have one OT question here: In TVB ROCH 1983 adaptation (and I suspect in the novel as well), when YiDeng first met YG and XLN, he had a chance to diagnose XLN's condition and he said that it was a pity that he had been injured by Kau Cheen Yan earlier so he could not use his Yiyang Finger to help delaying the effect of the venom in XLN's body. However, Kau Cheen Yan at that time was not injured although he used some of his power earlier. Why didn't YD teach Kau Cheen Yan his Yiyang's finger? Otherwise, with Kau Cheen Yan's internal energy, he should be able to help XLN.
KCY internal energy was ying based, YD's was yang (this was the reason why HR couldnt be saved by the 9yin manual, unlike GJ). YD couldnt teach KCY YYZ without neutralising his yin energy (similar to what ZWJ did with ZZR).
He obviously had it worse than most ppl. But it's a problem everyone can relate to on some level.
One of my complaints (and you know I have many) about ROCH is the way that Jin Yong portrays human emotions in this story: it's not that the author introduces unrecognizable, unrelatable feelings in his characters in this story, but that he takes them to such EXTREMES that what should be easily plausible and relatable becomes less so. This is a problem endemic to much of wuxia, but I feel that ROCH is particularly egregious about it.