A lot of points to respond to here. Unless someone is so atrocious that there is absolutely nothing I can think of to say to them that would encourage them, I point out something I think that they can build on, with a suggestion of how they might approach it differently.
And of course, Martin, you are assuming that your evaluation is Truth personified. That's a real dangerous approach to take, because some of the best musicians and artists who are now considered great were considered crap by some people. It's safer not to confuse personal opinion with absolute fact.

I had someone send me a long tape of many songs that they had written.. someone who admired my songwriting. It took me awhile to listen to the songs (which were very weak) to find some lines or approaches that I felt were good. This was someone who was in my aduience and sent me the cassette. I never met the person, or heard from them again, so I have no idea whether my encouragement and suggestions had any positive effect. In a way, that's not even the point. If I had just said, "your songs suck" I don't think that I would have accomplished anything positive. The person seemed modest and sincere in their efforts.

to Guest: I don't think anyone (other than a sadist) would actually encourage bad writting. There's a surplus of the stuff already.

Jerry