You're right it probably could have waited, but I understand Michael and everyone else's anxiousness over it. You saying they just want what they want makes it sound like Wiley was just getting a nose job or something silly. It's not like everyone was overjoyed at the prospect of Wiley having surgery. And, I think it does matter if the surgery was a success. Complications could have arisen, and that could have happened whether they waited or not, but it hasn't.
Michael doesn't get everything he wants - witness his string of dead girlfriends. I'm pretty sure it wasn't his desire to have his firstborn's mother be a psychopath. I hate Michael in most Corinthos-related scenes but am fine with him in most others. I'm okay with him losing now and then, but certainly not to Nelle.
Monica offered to get Nelle second opinions and Nelle wasn't interested, so no, she didn't just throw articles at her.
Willow isn't detaching from Wiley because his father knows Wiley loves her and wants her in his life. Willow has barely had any scenes with Wiley since she found out he wasn't her kid. She's not outside the Q mansion with binoculars watching Wiley constantly.
Willow and Nelle's actions aren't really comparable. Willow had a legitimate concern and was worried about what Shiloh would do to the baby. While the Corinthos clan certainly aren't safe to be around that wasn't Nelle's concern. If Michael had been willing to forgive her for her numerous lies she would have happily married into that family (and almost did) and stayed with him. She only tossed her kid over to Brad like he was some sort of tradeable baseball card because she wanted to stick it to Carly (and Michael for seeing who she was and being done with her.) She wants to win over her no matter what. That's what the current custody case is about as well.
They might not recognize it because they don't see it that way and I don't either. I don't think Willow is twisted at all. You're probably right she should be in therapy and deal with the death of her son, but it wouldn't change her feelings for Wiley. She loves him and sees what a toxic presence Nelle would be in his life and wants to protect him. There's nothing unhealthy about that. She's not delusional. She knows that WIley isn't her biological child, but that doesn't change her love for him. That's not sick. And, she was perfectly fine not marrying Michael. It was Sasha and Chase pushing her toward Michael that convinced her to help Michael.