You don’t get it. Science doesn’t actually care whether Kettlewell made mistakes. Science cares about what CAN be observed, reproduced, and analyzed. Kettlewell’s hypothesis was correct and this has been demonstrated by more rigorous experimentation, so that’s where science stops caring. Obsessing over potential failings in Kettlewell’s methodology is a pointlessly masturbatory witch hunt exercised solely for the purpose of muddying the waters. Given that creationists don’t even dispute the validity of natural selection, continuing to whine about it is beyond pointless.