I came across a few posts noting that Ed should not have told Stede not to kill Ned Low, which got me thinking...
I don't really agree with that. That entire scene, both Ed's decision and Stede's decision, is complicated with a lot of different things, but none of them quite so much as the shared knowledge, and pain, of both men. (Yeah, I'm not capable of not writing an essay.)
Stede is the only one who knows about Ed's father. Ed tells himself-as-Hornigold that he never told anyone about killing his father, and Hornigold reminds him: "But you did, though, didn't you? And he left you." Stede is also the only one who knows Ed really doesn't kill - that he, by his own admission, outsources the killing to others. The murder of his father is the center of Ed's self-loathing, and is the thing that he relates, in his conversation with Hornigold, most directly to Stede leaving him.
Low's insults don't affect Ed much; he's heard them before, he knows what's behind them. But Stede has been watching Low hurt people and things he loves - Ed, the crew, the ship itself - without being able to do anything about it. He successfully uses his "people positive management style" to get Low's crew to turn on him, but the problem of Low himself remains and cannot be eliminated in the same way.
Low calling Ed a "lowborn dirtbag" is what finally makes Stede snap, and one could argue that his response is more or less automatic. It's certainly emotional. There's nothing he could say to Low to put him in his place, as he did with the aristocrats in "Dressing Well." It wouldn't work; he cannot meet Low on a level playing field and use the same weapons against him, because Low's whole thing is being a bully and Stede is not a bully. Everyone, including Ed, is surprised when Stede actually draws his sword. But by the time he's done it, there's no going back.
Low obviously reads people quite well, and like many bullies he can suss out the places that will hurt others the most - he knows that torturing Stede will hurt Ed more than torturing Ed. He knows that insulting Ed will hurt Stede more than anything he could say to Stede himself. And he hits on Stede's fears about his masculinity and especially Ed's feelings about him. Low is another in a long line of bullies (Nigel, Chauncey, his father) from Stede's class, and he manages to hit exactly the sore spot, the fear that Ed only loves Stede because of his "bumbling amateur status."
Stede absolutely believes the things that others say about him. In the moment, Stede reads Ed's statement not to kill Low in exactly the way that Low wants him to - as a desire to keep him docile, pure, a pet. Not a real pirate, not a real man. He struggles with it - having gone so far as to hold Low at swordpoint and to force him onto the plank, it's hard to back down. His crew egg him on - Low does indeed deserve to die for what he's done. But when Stede kills Low, to the cheers of the crew, no one but the audience can see his face - the horror and shock at what he's done, as the memories of his childhood shoot across his mind.
As soon as Stede's actually committed the murder, he realizes the true meaning behind Ed's words, and it's this, combined with the shock of having truly, directly, and deliberately killed a man, that sends him running back to his cabin. Stede sees himself as a child, the boy who just wanted to pick flowers, splattered with blood from "men's work." He cannot go back now; he's made a choice, and he murdered a man. He does exactly what he's done each time his own shame has become too much for him, and hides himself.
But when Ed comes to his room, he directly relates it to his own trauma - "I was a wreck after my first kill as well. Well, it was my dad..." He's there not to shame Stede either for his violence or for his self-perceived weakness, but to be present for him.
That traumatic past is part of what unites them. Stede was forced to witness death and was told it was what men do; Ed committed murder, and has been haunted by it ever since. Ed sees the potential of the same thing happening to Stede - being so overcome with guilt and shame at actively committing murder that he suppresses and remakes his self to avoid coping with the horror of what he has done. It doesn't matter that Stede is a grown man and Ed was a child; Ed knows how badly it can warp someone, and Ed knows better than anyone how the abused child becomes the traumatized man. He tries to warn Stede first, recalling their past, and then he shows up for Stede in a way that no one did, or could, for him - not until Stede himself extended his hand and said, "I'm your friend." Ed is there at the door within minutes, asking if Stede is OK, offering his support, not letting him hide alone if he needs someone to hold him.
I've said a lot about the progress from the moment Ed appears at the door to the moment Stede closes the curtain here, but again I don't think it should be read as Stede proving his masculinity or Ed feeling sorry for him. Sex is not being treated frivolously here, either by the show or by the characters. It is an outpouring of pain and grief and deep, intense love between two men who understand each other's suffering at a fundamental level, who have shared things with each other that no one else knows, and who see all of each other, the darkness as well as the light.
