So what you're saying is, if I like it I can tell you but if I don't you don't want to hear it. So you basically don't want the truth. And it is courtesy, I could have read it and not commented. I find it ruder to not comment.
I comment loads of poems daily. I read so much poetry on this site that is just the same. So I came across yours, I read, and I commented. If I read peoples work I'll comment out of courtesy, but it doesn't mean I'm going to lie and say it's good if I don't think it is.