Questions regarding bounty hunters

If a bounty hunter suddenly infiltrates my world and I am in co-op with someone and we teamed up to attack the bounty hunter and we win. Are we wrong for doing that? or the bounty hunter just have some anger issues because he feels like teaming up against him is unfair?

If you are a bounty hunter and you see that we are in co-op, why do you still want to proceed with the hunt?