Wei Ming harbored no prejudice against Gao Xuan; in fact, he quite admired the young man.
So handsome, excellent in swordsmanship, and with a good personality, though just a bit of a scoundrel with women.
However, men, in most cases, are scoundrels. It's just that some don't have the ability to be, so they think they're pure-hearted boys. Give them three or five pretty girls, and they'll surely want them all.
Wei Ming didn't see this as a problem.
The natural world is like this; powerful males always get more females. In human society, having capability, money, power, talent, or even looks means obtaining more resources.
In his youth, he had more girlfriends than he could count. He wouldn't be too harsh on Gao Xuan either.
However, the thought of him hitting on his niece was something Wei Ming couldn't accept from Gao Xuan.
That's how rational humans are. They make distinctions between close and distant relationships.