Somebody please explain...

[Dr. Zeppers]

Keep in mind that a pirate killing lower level enemies, and following you along and attacking the same enemies you are may also be a young child. They arent trying to grief you they are just having fun, and recognize its harder when doing it alone so they play along with the others around them. Without taking a moment to be kind and explain first, it would be rude to simply tell them to "buzz off". With that in mind I have just made it a habit to usually 'move on' and leave them be.