OK, I understand that they're basically a stand-in for the Talon Company from Fallout 3.
That being said, Talon Company had been hired to kill the Lone Wanderer, so their actions in Fallout 3 were understandable.
I can't understand why the Gunners in Fallout 4 want to shoot everybody on sight. If they're mercenaries I ought to either be able to hire them or maybe even work for them.
How do they know I'm not a prospective customer walking up to their camp? Shooting me could be bad for business.
They seem to be little more than Raiders with better gear.