I've had this happen to me twice.
The first time was in an RAF Puma during a VIP trip on a military exercise. We had just dropped off the passengers rotors running when a labourer working in an adjacent field ran to the open cabin door.
The second was when a suspected criminal ran at the aircraft as I was landing.
On neither occasion did it seem sensible to attempt an aircraft shutdown, just the opposite in fact.
The fact that the chap involved in the case in this topic was waving his arms around put him in grave danger and I think the pilot was entirely correct in lifting off for that reason alone.