Yes, people disagree about what good poetry is. I view my own definition as wholly banal & likely to be accepted by everyone. Strong, memorable images and rhythms, poetry that does something with language--all that. I think it's inherent in the poetry that has become most canonical. The songs of Blake, or the musicality of Campion or Lorca, or the Odes of Keats or Haiku of Basho. The verbal wit of Quevedo.
Yet people disagree with me. I cannot force myself to believe that they are equally right, or entitled to their own taste, since in fact I cannot believe that. Belief is an interesting thing: it does not result from an act of will or decision. I cannot, for example, believe that Nebraska is to the South of me when I am in Kansas. I cannot simply choose to believe in the literal existence of the god Thor. I recognize, intellectually, that aesthetic judgment is subjective, but I know, with Kant, that this recognition of subjectivity has no effect on my actual feeling about such judgments as they pertain to me.
What is more: this judgment, and my superior judgment, is actually a finely honed ability of mine, one for which I have trained rigorously for many years. I believe that it is a critical tool. It allows me to perceive other things about literature that would be simply invisible to me if I weren't able to perceive that some poems are aesthetic failures. There is a reason for a failure, a cause, and looking at that cause allows us to make other judgments.
Imagine a musical critic who wasn't able to make judgments. He could (I am using masc. pronoun here because I am imagining him as a version of me) listen to music and analyze it. He could have a vast knowledge of it, in fact, on the theoretical level. Wouldn't we feel, though, that he was handicapped in some way? Even if the ultimate point were not to say what music is better than some other music, we would want him to know what people appreciate in the music of Debussy, and explain why some Debussy works better than other parts of it in producing that effect.
Judgment is neither the first not the last thing. Saying something is good or bad should not shut down a conversation, nor be simply assumed as background information.