The point is that he thought there was humor in rape/pedophilia at all / was fine to express this in social media, which makes a serious comment on his personality and lack of humanity. It does not matter if any of the individuals who read his tweets were not victims of either attack, its the fact he--apparently--did not give a damn that victims of those crimes actually exist when making his so-called "jokes". People have been fired for posting racist "jokes" none of the intended targets did not see or know about until it was uncovered some time later, but some employers feel merely having those beliefs made him/her undesirable / offensive as an employee, co-worker and potentially an explosive situation waiting to happen. If making despicable statements is so important to some, they should be prepared for and accept action against them from an employer, not to mention longstanding, deserved damage their public image.
"Lack of humanity"?
Geeze, won't someone please think of the children much?