Flagging for disagreement on rewards is considered a valid reason to flag/downvote. I think a large part of the problem is the perception of getting flagged is that someone did something wrong, and that a lot of times it is taken personally (even though in reality, getting flagged does not necessarily mean that the person did something wrong).

It seems that many in community are moving more towards subjective flagging - which is allowed, but may take some time for the community to adjust to.