Consider a consequentialist student being tempted to cheat on a test. Getting a good grade is important to him, and he can only do that if he cheats; cheating will make him significantly happier. His school trusts its students, so he’s pretty sure he won’t get caught, and the test isn’t curved, so no one else will be hurt by him getting a good score. He decides to cheat, reasoning that it’s at least morally neutral, if not a moral imperative – after all, his cheating will increase the world’s utility.

Vlad has discussed below some of the problems with this claim. But there's a more serious issue: even under causal decision theory it is likely that such cheating will not increase the overall utility. Furture employers will look at his transcript. If they are hiring someone who is less qualified because that person cheated then they may not do the job as well as another individual.

ETA: Thinking about this slightly more, it sounds like you are trying to construct a least convenient world. In that case, your argument might go through.