Marines are not only trained to be aggresive they are highly disciplined. Plenty of soldiers in recent and past history have been assigned to roles outside their sphere of training. I do not know that as a defense used in a court (outside of incompetence for a task at hand like not being trained in the system resulting in damage), for a moral decision ones specialty is not generally taken into account.

However we have already see battlefield duress as a reason for a cup of tea and a lie down even if it was for killing prisoners...

I assume the SAS are at a whole other level of aggression and control then normal troops... yet they are the first pick for peacekeeper missions for the UN by the nations that field them.