Why? They're both acts of violence that people gloated over. He's not saying "killing this guy is just as bad as lynching innocent black people". He's saying America likes killing, whether it's someone you think should be killed or not.
There's still a pretty big difference between violence against random innocents and violent "revenge" against a powerful force. I'm sure people would also be thrilled if an insurance bigwig got sent to prison, or tarred and feathered, or humiliated in some other way.
He isn't comparing them. He's using the casual and festive nature of many lynchings as support for his argument that America has long embraced extrajudicial killing.
Lynchings were not always reserved for blacks nor were they solely conducted by whites. It's also not an American thing, it is human nature and exactly why we have a legal system. There were some racially motivated lynchings of course but to reduce it to that is misleading. Approximately 40% of lynching victims were not black.
