MCU is the biggest movie franchise ever and no other franchise has had a 100% Critical & Box office success rate with 20 movies being out there. Marvel is mostly known for their light-hearted fun movies but from what we have learned starting from Civil War is that they can actually be darker at times. Disney obviously releases PG 13 movies while Spider-Man: Homecoming was targeted for a younger audience base, still the heroes sometimes end up continuing on darker paths in order to save the day. So if it means that someone has to die for the greater good, the heroes don’t step back and are rather ready to pay the price of being a hero.
The no killing rule goes for almost every Superhero but lately, no one has been following it. It is crazy to even think about the fact that not even Batman, who is the first guy that comes to our mind when it comes to following the no Killing rule. Batman is big on Justice, and in the MCU you will find very similar motivations in Daredevil. The two heroes are very similar in many cases, but Snyder’s Batman was not afraid to kill. Snyder gave a justification that Batman did not directly kill anyone, rather he did things that led to someone dying, but if you watch Batman V Superman, he was actually on a killing spree!
Nolan’s Batman was not innocent in this case as well even though he followed the strict no killing rule. While in the MCU, no one ever says it out loud that they won’t kill, but they do believe in saving lives and providing people a second chance instead of being Judge, Jury and Executioner. Still, that doesn’t mean that they are innocent of killing.
In fact, if you think about it, there are only a few heroes who have not killed anyone in the movies they have been in. It is just that these movies actually cover all the darkness with funny scenes to follow up. Heroes like the Winter Soldier, Black Widow, Iron Man, Thor, Hulk and even Captain America have killed without a second thought. They have been portrayed fighting armies, whether those were aliens, murder bots or even humans from Hydra, they have all killed.
The Iron Man suits are killing machines and both Rhodey and Tony are guilty of killing. Natasha was a Russian spy so she might have killed even before she joined SHIELD. Cap’s been in World War II so his kill count may actually be bigger than any other Superhero on Earth. Falcon goes around shooting people, so guilty! Vision killed Ultron on his second day after being born. Thor has admitted to killing more than 3000 people/aliens/robots. Black Panther was after the life of Bucky, but he forgave him. Other than that he killed Erik Killmonger, his own Wakandan people (maybe) and the Outriders.
The Guardians killed Ronan, Thor killed Malekith, Ant-Man killed Yellow Jacket, Wanda and Quicksilver have killed Robots and they have attempted to kill the Avengers. Wanda went on to kill the outriders, she killed Proxima Midnight and she even killed Vision (even though it was undone).
So technically, everyone in the MCU has killed off certain people, except for two – Spider-Man and the Wasp. You may argue that Mantis has not killed anyone, but she literally had a direct hand in killing Ego, so she is guilty. Spider-Man and the Wasp, on the other hand, have not killed anyone.
Spidey gave Stark a plan to kill Ebony Maw alien style, but he did not have anything to do with technically killing him off. He even has a Kill mode in his suit which he refuses to use. The Wasp has bruised and broken bones of many thugs who worked for Sonny Burch, but she has not technically killed anyone. So Spidey and the Wasp, two bugs who can kill people with their sting/venom haven’t killed anyone yet!
There may be an argument that Quicksilver might not have killed anyone as he just broke down Ultron bots but the artificial intelligence was still alive. So he may not be charged with murder. He sure is guilty for an attempt to murder!
Still, the fact is that no one is purely innocent!