Very interesting question and the answer is rather long and complex, but here are a few ideas to get you started.
Plato saw Philosophy to be opposed to Poetry and Rhetoric. In fact, he alludes to the "ancient quarrel" between these two sides, as he saw them. One of the ironies concerning Plato is that despite his unremitting hostility towards poetry and rhetoric, he is famous for his own poems and rhetoric. Go figure!
Plato, in his work, Republic, attacks viciously the poetry of Homer and those who support it. He addresses his remarks at the "praisers of Homer who say that this poet educated Greece, and that in the management and education of human affairs it is worthwhile to take him up for study and for living, by arranging one's whole life according to this poet”. Plato seems to be setting himself up against the entire worldview that Homer and his followers have created and sustained. He argues that the influence of poetry is pervasive and often damaging, and that the ideas it presents about nature and the divine are often mistaken.
Although Plato acknowledges the usefulness of poetry, in education, in civil celebrations etc, he regards it at all times with suspicion. Although he recognises poetry is a vital and necessary part of human society, he sees it as a mark of humanity's fallen state. Of course, his remarks must be read within the cultural framework of Plato's time, where the dissemination and spread of poetry was very different.