Cheating is the only way some students get through particularly hard tests or assignments. Some knowledge of the topic given is required to ensure that the answers the students obtain are factual. Cheating isn't easy; it takes a very specific skill set to be able to cheat without being caught, which can be used in jobs requiring spying on a rival company or such.
They would get too used to cheating and cheating would be the beginning of their dishonesty. "Honesty is the best policy!" They would probably go into their next grade not knowing anything. It would also deflect students form finding what they truly love. Sometimes cheating is the easy way out but you shouldn't want the easy way, you should want the BEST way.
Cheaters learn nothing because all they do is copy someone elses work and they don't do it themselves. Either that or they're just really lazy and don't feel like doing the work themselves. But no if schools were more tolerant on cheaters then more people would cheat and nobody would learn anything