I think I'm going to tell a new writer that they aren't any good and they should quit writing.
Why are you going to discourage their writing?
He's just a bad writer and I I'm annoyed by the things he writes.
Of course not everyone is a great writer, but that is no reason to discourage them from trying to improve. Instead of discouraging them from writing, you should give them some honest feedback and let them know how they can improve their writing. You should use your knowledge to help them get better, not bring them down.
I just don't like to see amateurs get attention from writing.
I believe that every great legend comes from humble beginnings. It will pay off to be patient with them, they have a lot to learn and if you support them, they might write the next hit!