Project managers want to avoid scope creep because it's a vicious circle. You have one change request, triggering another, which in turn triggers another, until the project baseline is rendered meaningless and unusable.
Scope creep is never good and never fun, it almost certainly delays the project and increases (often substantially) the cost of the project, and SHOULD be avoided. There is no positive side to scope creep.
Scope creep a sign of a bad and a weak project manager, a project manager who is unable to confront the client, and who stinks at managing requirements and controlling changes.
"prove he's worth his salt..." I think that ship had already sailed once you have scope creep. The only think that the project manager can do is to some damage control to save his some of his remaining reputation.