I understand why
they did it, but you'd be correct in that...it really doesn't apply. Just because someone is evil, doesn't mean they should show Sith Corruption. Tons of theories and other such stuff Lore-wise...but yeah.
And wow...I didn't know you could turn it off! I'm doing that the moment I get back. I like my BH without corruption thank you very much. Was actually disappointed that he started even showing corruption as I'm sitting there going, "He's not force sensitive...why is this showing up??"