Andrew Z. answered 03/21/19
Experienced MFA Grad Teaching English, Literature and Writing
The phrase "on someone's behalf" actually means doing something for someone in place of them doing it themselves. It is entirely possible for this phrase to have a positive reading, it just depends on context.
Here's are some examples: "He accepted the punishment on my behalf, sparing me the agony I would face otherwise."
"My brother is having a tough time with this essay, so I'm writing it on his behalf."