This is a good question, because it seems like cheaters get away and often time they even seem to get ahead. But I would say that cheating hurts everyone for three reasons.
First, when someone cheats to get ahead, it is a false indication of his or her intelligence or skill. So, when this person gets ahead in this way, he or she may not be able to perform and hurt whatever he or she is doing. If this person is working for society and got ahead by cheating, it will harm society. Think about a doctor that cheated his or her way through medical school. Dangerous, to say the least.
Second, those who did not cheat but studied may not get to where they should be, because they have been overlooked by the cheaters. This also harms society.
Third, cheating creates a culture where there needs to be extra careful enforcement of ethics. This breaks down trust. When this happens, we may have to live in a society of skepticism.