Sexually abusing kids. It's so unnatural that no other species does it.

When the culprit is an adult, ideally, some form of shunning would be the best punishment. People who do that are probably always narcissists who crave attention and respect; depriving them of that is the best punishment possible. When the culprit is a teen, like Josh Duggar, he should get counseling in the hopes of curbing the behavior AND sorting out his own issues, because it's a good bet some big trauma befell him to get him to act that way in the first place. (He wasn't "curious", like his parents said: curious is when you try to get a peek, not cop a feel.)