Founders of major martial arts sects tend to be great people. One doesn't become the founder of a sect that wins the respect of wulin at large unless one has the requisite martial, intellectual, and moral acumen. Central Divinity Wong Chung Yeung, Cheung 3 Fung, and Gwok Seung each were great individuals who founded great martial arts and religious sects (the Cheun Jen Sect, the Mo Dong Sect, and the Ngor Mei Sect, respectively).
In each case, the founders were able to personally train a succeeding generation that did them honor. Whatever criticisms one might have with the Cheun Jen 7 Disciples, none of them ever became a coward, traitor, or rapist. The Mo Dong 7 Heroes were each and every one an honorable, courageous, and capable wulin gentleman. Not much is known about the second generation Ngor Mei Sect Leader who directly succeeded Gwok Seung, but she was unlikely to have been an abominable person.
But the third generation...that's when all the bad seeds start showing up.
The third generation of Cheun Jen Sect produced a rapist and two traitors (Wan Tze Ping/Yan Tze Bing, Yeung Hong, and Chiu Tze Ging).
The third generation of Mo Dong Sect produced a coward and traitor, Sung Ching Sheu.
The third generation of Ngor Mei Sect produced a vindictive, cruel, and hypocritical leader - Mit Jeut See Tai, whose failings would live on after her to stain the succeeding fourth generation as well.
Stretching this model further, the third generation of the Ancient Tomb Sect produced Lee Mok Sau.
What is it about the third generation of a sect that brings out all the bad seeds?