On the face of it a very unpleasant experience. Clearly any threat is unacceptable- assuming, as I do, that it was a threat of some sort of violence. That seems to me to be a pretty good reason to offload. However it's wrong to criticise the Captain (other than the poster who was actually on board) because he will have had more facts and info to go on than those on here.

Also the initial incident, before the threat was made, is unclear. What was said and what was the context? Who was the person being abusive to and why? It's not correct behaviour full stop, but in order to determine whether it's so serious as to warrant an offload does, in fairness, require more detail.