I wouldn't even say don't let people who have killed in, the basic line I think we should take is to look at it on a case by case basis. If they understand that what they did was wrong, they embrace marxism-leninism and they haven't killed or tortured civilians we should let them in.
You started with "Should the cops who killed unarmed black men let into the party?" I responded with "no those who commit war crimes (implying that we shouldn't let cops who murder unarmed black men or are complicit in that either) shouldn't be let in." You then said that "every troop in Iraq was a criminal" implying that all ex-cops shouldn't be let in as well. If you make a comparison between cops and soldiers, follow through. You're trying to get me to make your point for you by answering each question one at a time, just make your point.