Padme was not a Witness
I will never join the “Padmé was stupid to go to Mustafar” parade—she had valid reason to believe in the possibility of Anakin’s redemption—but there’s something awful in the fact that she didn’t have to witness either of his massacres.
Obi-Wan and Yoda walk past the bodies of their people—of their people’s children. Bail Organa goes to the temple and sees a kid get shot down trying to escape (more clones than Anakin, but still).
Padme hears about the second massacre after sitting in her apartment while the Temple was on fire. She’s told about them in vague terms. “I killed them like animals,” “he killed younglings,” She has a touch of denial when she goes to Mustafar partly because of her belief in Anakin, but partly because—I think—the Tuskan Massacre was never fully real to her. She understands it intellectually of course, but violence on that scale is difficult to conceptualise without seeing it, especially if it’s easier to just let it go. If she’d seen the bodies? Or seen Anakin kill them? She watched that one refugee kid die slowly, not at all violently, when she was working with the refugee organisation, and it affected her for the rest of her life. It is not a lack of caring on Padmé’s part that’s the problem.
Imagine being Obi-Wan listening to Padme saying “there’s still good in him,” after walking through the Temple, seeing the lightsaber marks on knights and children alike—not even to mention seeing her get strangled. It sounds not only wild, but honestly deeply offensive on more levels than one (besides the obvious issues it’s another, “train the boy,” prioritise Anakin over everything moment, except this time Obi-wan’s entire world has been torn apart, rather than just losing his Master)
If Padmé had actually been a witness to Anakin’s violence? If it was made present and visceral to her?
I think her opinions and her actions would’ve been different.
Thematically, it is crucial that when Luke goes to the second Death Star, he is under no illusions about who Anakin is or what he’s done, and in his most desperate moment he chooses to ask Anakin for help anyway. Padmé goes to him still a bit in denial, still a bit convinced things can return to how they once were. When she starts to push at the illusion, Anakin accuses her of betraying him and strangles her to shut her up, attempting to preserve the illusion (the difference between Anakin’s state at the time of his confrontations with Padmé and Luke is a whole other, very important topic). In part, her illusion allows Anakin to believe he can preserve the past (to be clear—he is the only one responsible for the choice to strangle her; Padme being imperfect is not an excuse for domestic abuse).
- Side note, but if anyone is not sufficiently freaked out by Anakin strangling Padmé, it's important to know that strangulation is one of the flashing red warnings that physical abuse is doing to turn deadly, very, very quickly.
Luke’s complete and honest knowledge of Anakin’s worst self means there is nothing for Anakin to lose except his son, exactly as he is. No illusions, no wonderful past, not even any good memories together. Just his son.
To me, that’s one of several reasons (both thematic and logistical) why Padmé’s plea fails where Luke’s succeeds. None of those reasons has anything to do with her being stupid to go in the first place.
(There are some wonderful fanfics out there that show Padmé actually making her disapproval about the Tuskan massacre—both despite and because of her love—actively known during their marriage, and I think that interpretation of her is a stronger character than ROTS gives us, and more in line with what we’re shown in the first movie)