Tanks!!!: Grit explaining to Adder that yes, he isn't particularly loyal to Blue Moon and yes, he doesn't care much about what land belongs to which country. But the destruction of cities and killing of civilians is unforgivable.
Duty and Honour: Black Hole has set up laser cannons around several strategically unimportant Yellow Comet cities which are under siege. Kanbei knows it's a trap, but goes in anyway because it is his duty to protect the people of Yellow Comet.
COs don't sit idly by and watch their people be destroyed! Even if it's a trap. Even if it's strategically unimportant.
Hawke or Jake shooting Von Bolt's chair in Dual Strike, forcing him to live out the rest of his life under his own power... which probably won't be very long. Jake's line after doing so is pretty good:
You don't get to die while the rest of us clean up your mess!
Lin receives one of her own after defeating Admiral Greyfield in battle, while confronting him. He surrenders out of desperation, and claims that as he is now a prisoner of war, if she kills him out of revenge, she will be the same as him (as their original rebellion was caused by this same crime). Her response?