Some wuxia martial arts get so associated with their practitioners and their deeds that they acquire a reputation for being "evil" martial arts, even though there's nothing necessarily evil about the techniques themselves. Let's explore a few of these.
1. 9 Yum White Bone Claws: this skill acquired its unsavory reputation for how Chan Yeun Fung and Mui Chiu Fung trained in it and how the likes of Yeung Hong and Chow Chi Yerk used it for murder and mayhem. Though it was brutal, the 9 Yum White Bone Claws wasn't innately evil, and possibly could be used in more heroic and merciful ways.
2. Qwai Fa Bo Deen: this skill acquired its reputation largely due to the heavy personal cost that its practitioners had to pay to train in it. That aside, it doesn't seem to be inherently evil. Nothing about it seems to establish that it cannot be used heroically.
3. Keen Kwun Dai Loi Yee: mainly got its reputation for being a foreign (Persian) skill associated with the Ming Cult, which had horrible relations with mainstream orthodox wulin for decades. Otherwise, nothing particularly evil about it.
4. Ha Mo Gung: associated with West Poison Au Yeung Fung and his nephew/son Au Yeung Hak, who were wulin pariahs. Moreover, the skill looked weird as hell and incorporated the use of poisons, but...it's still not necessarily evil.
5. The martial arts of Peach Blossom Island: once again, East Heretic Wong Yerk See had horrible relations with mainstream wulin and thus, his martial arts techniques were judged as "evil," but as his reputation improved during ROCH times, it seemed that Peach Blossom Island martial arts became associated with heroes rather than menaces.
Now there were a few martial arts which probably deserved their reputation as evil, beyond who used them and how. For example, the martial arts of Ding Chun Chou and his Sing Suk Sect acolytes in DGSD seemed to be completely inhumane, and I can't see how their skills can be used honorably, compassionately, and heroically. Ditto the Yeun Ming Divine Palms practiced by the Yeun Ming Elders in HSDS.