I actually like the idea that maglor was very much against all the kinslayings before they happened, each time fighting against it as hard as he could before capitulating in the face of his brothers' determination. I think his tendency towards despair and his avoidance of death actually helped him out at that point, the oath couldn't pull at him as hard because he was fully convinced there was no chance anyways and he didn't want to die.
I like to think each of the brothers had their own reasons driving them forward actually (yknow beyond the soul binding oath and the looming threat of the super-void and all). Maedhros did it because he couldn't see any other way out after fingon. He had played every card in his deck and it all turned to dust, now he was simply in too deep. The sunk ship fallacy at its finest. Celegorm was the most genuinely consumed by the oath towards the end, giving himself over to it entirely like an animal becomes consumed when rabid. Curufin wanted to save their father and the more the others started resenting feanor, the more he felt it was up to him to stay loyal and true. Caranthir was the most like maglor, but also had a closer connection to life and feared what would come if they didn't succeed. Ambarussa wanted to protect each other—the others too ofc but each other most of all.
And maglor? A lifetime of being someone else's second, of playing the caretaker, of repeated attempts of leadership that were ultimately miserable experiences—he gave himself over. Not willing to lose more, he clung onto what he had left no matter what. I think maglor represents how sometimes compliance and loyalty are violent—that standing aside and letting others dictate your life is ultimately also a choice you make with consequences attached.
I also don't think this side of him softens his character at all. Because the crux of the matter is, he still did them. Yes, the first one was out of confusion and loyalty towards his father. Yes, the others were commited only for the sake of his brothers. Yes, it was all because he refused to betray his family. But do any of his victims know that? Do they care? Did he kill any less because of it? Or did loyalty drive him to fight even harder? The act of it remains, even if his reasons were different and even if he was reluctant. And no matter what their reasons were, senseless slaughter is the act all the sons of feanor commited. I think giving them individualized reasons just sweetens the pot and brings more color to his later actions
