Though she's a super-spy who often plays both sides, Iron Man 2, Natasha Romanoff has been positioned as someone who operates in a moral gray area. Her very background says as much, with her starting out as a Russian spy brought up in the infamous Red Room only to leave the Black Widow behind and defect to the United States, where she became a S.H.I.E.L.D. agent thanks to Hawkeye's intervention.
Even after becoming Captain America: Civil War when he snaps, trying to hurt Natasha, "Boy, it must be hard to shake the double agent thing, huh? Sticks in the DNA."
They're wrong about her, though. Over the years, as Natasha has grown more comfortable with being an Avenger and closer to her teammates, she's proven herself to be the most stalwart and loyal Avenger of them all. For years, she's helped Captain America co-lead the team. When he and Avengers: Endgame, it is Natasha who sacrifices herself to gain the Soul Stone needed to defeat Thanos once and for all. For those reasons and more, Natasha is actually the most moral Avenger, the one whose sense of right and wrong is most needed in modern times.
Her Background Has Made Her Kind, Not Nice
There is a marked difference between being nice and being kind. The first is surface; the pleasantries exchanged with a stranger, the front put on in front of a disliked coworker to keep things professional. The latter is born out of thoughtfulness and a real ability to read a situation, and "kind" and "nice" can't always exist at the same time. Natasha's training has made her able to read people and situations easily. Gauging a person's feelings is often how she stays alive. While that can be used to manipulate a situation and bend it to her will, it can also be used as a tool to measure how a friend or teammate is doing and what they might need at any given moment.
Natasha's comion has served her well. When Peggy Carter finally es away of old age, Sam Wilson travels with Steve Rogers, but i's Natasha who shows up on her own in London for him. She comes not as Black Widow giving Captain America a warning about the Sokovia Accords, but simply as his friend who recognizes he might need someone to him in his grief. "I didn't want you to be alone," she says before pulling him into a hug. Steve has always kept his love of Peggy close to his chest, not often speaking about her. Black Widow is his one teammate who figured out what exactly Peggy and Steve had been to each other and knows how devastating the loss would be.
But Natasha also understands that sometimes to be kind, she can't be nice. Sometimes the situation calls for a little ruthlessness. She's the only one on the team able to calm Hulk down after a rampage by singing him a lullaby; she knows how much Avengers: Age of Ultron comes down to a choice between not hurting Bruce and saving thousands of civilians, she doesn't hesitate to push Bruce off a ledge to trigger his transformation into the Hulk. "I adore you," she says, kissing him. "But I need the other guy." Just then, his feelings don't matter; the lives of the civilians do. Captain America might have tried to reason with Bruce. Iron Man would have mocked him or gotten annoyed. Both ways would have wasted time. Black Widow simply gets the job done without hesitation because it's the right thing to do in that situation.
Tony And Steve Are Too Rigid In Their Beliefs & It Hurts The Team
Captain America and Iron Man have always been seen as the leaders of the Avengers. Steve Rogers and Tony Stark are the two moral poles between which the team is hung, and whose decisions have driven most of the Avengers' action–often to the team's detriment. That's not to say they're not good men, but they're rigid ones and their unwavering belief in the rightness of their beliefs means both of them have, at times, been unable to adjust when a situation has called for it. They're the quintessential unstoppable force and immovable object, and the Avengers get caught in the middle–and so does the world.
Tony is often the arsonist and fireman, and he has no idea where the line between "hero" and "potential supervillain" is when it comes to his obsessive pursuit of scientific knowledge. His meddling with A.I. without the knowledge of the rest of the team is what leads to the creation of Ultron and the necessity for the Sokovia Accords in the first place. As Wanda Maximoff rightly points out, "Ultron can't see the difference between saving the world and destroying it. Where do you think he gets that?" Tony genuinely wants to do good, but he trips over his own ego far too often.
As for Steve Rogers, his old-fashioned values sometimes keep him from seeing the world how it truly is. His singleminded determination to protect Bucky Barnes helps break up the Avengers. He disregards his teammates, his friends, and the team as a whole to protect another friend. Likewise, his insistence that Vision not be sacrificed to destroy the Mind Stone, while noble, can be seen as incredibly naive considering the alternative facing them: Thanos getting the Mind Stone and wiping out half of life in the universe, which is exactly what happens.
Natasha Sees The Shades Of Gray In A Situation
Tony's ego gets in the way and Steve's old-fashioned values get in the way, but Natasha has neither an ego or an old-fashioned mindset, and it enables her to assess a situation with clear eyes and do what needs to be done. It would be great if two adversaries could come to a gentlemen's agreement they never break, or no villains would ever take advantage of the Sokovia Accords, but that's not the world the Avengers live in. Modern times are not so black-and-white, and in order to protect the world, the Avengers can't be, either. Natasha is the one who understands that best because she has been a villain, antihero, hero, and everything in between. She understands how villains operate because she used to be one, and she knows that sometimes in order to defeat evil, you have to play a little dirty. Her underhanded methods get the Project Insight data off the Lemurian Star for Nick Fury, they con Loki out of giving up his plan on the Helicarrier, and they bring down Alexander Pierce and Hydra within S.H.I.E.L.D.
It's also her ability to see the shades of gray that enables the Avengers to defeat Thanos in the first place. Had she not let Captain America and the Winter Soldier go during the airport battle in Civil War, they and the rest of their team would have been locked up in the custody of the U.S. government when Thanos attacked. Half the Avengers would have been on the bench or behind bars and utterly helpless to do anything as Thanos laid waste to the world.
Black Widow may not foresee the threat of Thanos when she decides to turn a blind eye to Steve and Bucky escaping, but she recognizes the wisdom in letting them flee. Legally, according to Black Widow making choices that seem immoral in the moment but that turn out to be the right thing to do is a recurring theme in the MCU. Modern heroes call for a modern sense of ethics and it's why Natasha Romanoff is actually the most moral Avenger of all.
