I don't believe that's the case. He tried to avoid service by applying for a student deferral. When that application was denied, he enlisted. I'll try to find the thread that shows he was anti-war before he went in. There have been so many threads on him, it may take a while to find it.
Regarding the circumstances of his transfer stateside:
The officers who suggested his departure may not have shared their views and actions with all of their fellow officers. Another officer, not knowing what they had done, could have easily assumed that kerry's rapid departure was the result of his own initiative. Even if the others had suggested that he leave, he had to apply for the transfer himself. They couldn't do it for him.
After several weeks of being counseled about his actions, he probably decided that he'd had enough (who are these middle-class nimrods, talking to ME like this!). He acquired his 3rd Purple Heart and finagled his departure. Sounds like those in the know were only too glad to see the arrogant little SOB leave.