Our military is trained to kill the enemy. If there are plenty of dead "enemy" on the battlefields of Fallujah, Mosul, etc., then they are doing the job they were trained for. If you want a happy face put on discussions of war, talk to a politician.
If you don't get this, rent "Patton" and watch it several times over. And if you still don't get it, just sit back quietly (= STFU) and enjoy the peace and security your military affords you, despite the low pay and sacrifices they make.
Patton and Sherman were also needlessly criticized during their active duty. Both proved to have been officers of outstanding merit (only after they died). That shouldn't happen to Mattis. Mattis advanced his Marines faster and farhter than any other Marine Unit in the history of the Marine Corps (on one MRE ration a day - and with no cots, no running water).