User blog comment:IamJakuhoRaikoben/Chapter 368: The Third Seal, Review./@comment-24467372-20140126164811/@comment-178.148.174.152-20140127174328

"I seriously doubt that any FT member would be willing to commit suicide." - Gray, Erza, Loke. Okay, Loke didn't really want to commit suicide, but he also wanted to die and begged Lucy not to save him. Gray tried to commit suicide twice before Natsu stopped him and Erza was willing to die with Jellal back at the tower because she felt bad about not being able to save him, and later she would've sacrificed herself if Natsu didn't save her.

I agree that Ultear changed his personality completely, but like you said she still didn't controll him like a marionette. She just changed him from good to evil, and his intelligence has nothing to do with that.