I'm a little torn on this as well, but I think I'm in the author's camp:
1. The person making the change to the code for their purpose may not have the required overall understanding to execute a refactor.
2. I believe in a One Change At A Time policy: I'd like to be able to, at least in theory, measure the effects of any change. If you slap two changes together, that becomes difficult or impossible.
3. The person making the change has a purpose in making that change, and likely has committed to some sort of schedule or timeline for getting the work done. Forcing them to play janitor could easily derail that.
4. The change at hand might just be a small piece in a larger body of work, and shifting focus to a refactor would be disruptive.
Having said that, I do often take the initiative in doing refactors when making a change, if it makes sense to me to do so. But I don't think it makes sense to push that expectation on others. Hell, it's possible/likely that the person making the change has noticed the opportunity for a refactor, but has decided against it for whatever reason.
I might suggest a refactor in a code review, but couched with language that it's entirely optional, and won't block merge of the change as-is if the author decides it's not the right call for them.