Why should we agree with view of Plato's on poetry and poet ?
I am not so sure that we should agree with Plato. As you probably know Plato is pretty harsh when it comes to poets. Let me give you Plato's rationale and then answer why we should agree or disagree with him.
Plato states that we should banish poets for three reason. First, poets deal in shadows and derivative things. They do not know the unchangeable forms and so cannot encourage people to know them as well. Second, Plato argues that poetry makes people imitate the appetitive part of the soul, the very part that needs to be guided by the rationale part of the soul. Finally, Plato states that on account of point two, people become worse off. So, according to Plato, the banishment of poets and poetry is a necessary action.
Now should we agree? To some extent, I can see what Plato is saying. Too much of "poetry" and "creativity" seems to be a license to put your mind on hold and embrace sensuality for sensuality sake. However, there are times when poetry raises a person's mind to sublime heights. In light of this, what we need is good poetry not no poetry.