well..your right about some hacks not being good on the progressing hacks, but saying its rubbish its the kind of thing that just kills all their confidence in themselves, so to better make them improve, just explain to them what they are doing is not good, and maybe explain further on what to change, maybe link them to some threads that can help them, thanks to the map rating review thread, i learned a few things from other people who had more experience than me, and well, you didn't want to see my old maps, lol, they sucked, but no one ever told me "your maps are horrible, you should just give up,) they helped me out in what i needed to fix and sometimes a good teacher creates a good student :) heck, they might suddenly appear as one of the best mappers/scripters/spriters/etc ever, and thats thanks to all those who didn't give up on them, and helped them when they didn't know right from wrong. well, that was a lot of typing lol.
EDIT: and if you teach someone how to improve, and they still don't learn, then yea, then you can tell them off.