It also lets the liar try to trap rebuttals with gotchas. In this case, “so you’re saying there aren’t a higher percentage of black people in prison? A-ha! Facts, not feelings!”, or something stupid like that. Then you have to waste time with that, to which they’ll reply, “so you admit they’re more likely, a-ha!”

I’ve found it more effective to just say “you’re wrong” and move on. The end result of the argument is the same, and it gets them all riled up, which is generally what they’d hoped to inflict on others.