I was always annoyed that the A-Team never killed anyone.
Why? Killing is bad. And the show was essentially a cartoon anyway. It was light-hearted fun. Treating death as a subject of goofy fun would've been in poor taste.
Especially given that many of the times they could've killed someone it would've been in obvious self defense and it was against people who were murderers themselves.
No, it would not have been self-defense, because the A-Team were deliberately going after those people. Legally speaking, homicide can only be justified as self-defense if it's your only choice, like if you're trapped in a room or backed against a wall and don't have the option to run away, or if it's the only way to save someone else from immediate mortal danger. The A-Team were hired to confront and take down the people in question. They weren't cornered with no other option; they deliberately sought out and provoked the confrontation in the first place, and that negates self-defense.
Moreover, since they were hired to go after the bad guys, if they'd killed them intentionally, that would've been premeditated murder for hire, a very serious crime. Even if they went in without the intention to kill but ended up killing in the heat of the moment, it would still be murder, because their vigilante activities and use of firearms are themselves illegal acts, and killing during the commission of a dangerous felony, even by accident, is charged as murder under felony murder laws.
So there's good reason for the A-Team not to kill. They're already wanted felons for a crime they didn't commit, but they could theoretically clear their names and go free. If they killed, then they'd be guilty of a genuine, very serious crime, and there'd be no going back from that.
Not to mention that they're loyal United States military personnel, and thus presumably have no desire to take the lives of US citizens, even criminals.
After a couple of years, there is no way the A-Team would've had any kind of fearsome reputation left if they never killed anyone.
It's not as if anything else about the show made sense. (Like, how come the staff at the VA hospital never recognized Face even after he'd broken Murdock out dozens of times before?)