I am really not sure how this question is any different than your question that you asked about this poem a few days ago. After all, once you know the meaning of a poem, then presumably you know why the author wrote it. I assume that an author writes a poem to get his or her message across (in addition to wanting money, like the second answer from your previous question said).
So, I assume that cummings purpose in writing this poem was to criticize blind patriotism. I assume that he felt that blind patriotism is a danger to the world and that he wanted to push people more towards thinking about what patriotism should (in cummings' mind) mean.
I should point out that this poem was published in 1926, at a time when many American intellectuals were disturbed by the way that patriotism had been used to promote WWI and to suppress radical ideas within the US.