Thing is: nobody threatened to murder him, no one called for a boycott of Y Combinator. Nobody did anything except disagree with him. Somehow an insignificant fraction of humanity disagreeing with him was too much for him to deal with though.
It is probably difficult to voice an unpopular opinion and have it be met with so much derision by people whose opinions on business matters you respect so deeply. Unfortunately it is quite common for a pragmatic and reasonable professionals to have less than reasonable personal beliefs. Sam cares about what people think about him which is healthy and separates him from the sociopaths of the world.
