In reading the poem, I think that there is a definite stress to seek to eliminate the idea of boundaries that divide and set one individual or group of individuals against another. I would suggest that this is something to be avoided, it does not discount the idea that diversity in all of its forms is a good thing. Intellectual, spiritual, moral, psychological, and even temperamental diversity helps to reflect the complex nature of human beings. I am not entirely willing to embrace a view where all notions of diversity are eliminated for fear of differences. It seems to me that the challenge is to ensure that diversity is managed in a setting where disagreements and differences are not wedges that represent being violently disagreeable, to paraphrase Dr. King.
The following link takes you to an enotes question and answer about this poem. I would have to agree with the other posters that this poem wants us to look at each other as individuals and not members of a foreign country or even from other political or religious views.
I read the poem and got the impression that it wants us to consider all peoples of the earth as one humanity, regardless of nationalities, languages, skin color, creeds, or religious beliefs. It calls for universal brotherhood and an end to all the wars, hatred, and bloodshed that has gone on for centuries and is still going on. And what's wrong with that? I don't know how it will ever be accomplished or that it can ever be accomplished, but it is a wonderful dream, isn't it?
I haven't read this poem, but I am reminded of a quote which I have heard all my life regarding people other than white Anglo-Saxons like myself--"beneath the skin color, we all bleed red." Just studying basic anatomy, we notice that no matter a person's nationality, every person has the same basic physical makeup (making exceptions for disfiguring issues, accidents, etc.) One head with two eyes, a nose, eyebrows, mouth, and two ears; a torso with two arms, two hands, and ten fingers; two legs with two feet attached and ten toes. Inside, blood is red, and everyone has the same organs--heart, lungs, liver, sexual organs ( specific to being male or female), muscle tissue, arteries, veins, nerves, etc.
Shouldn't this be enough to prove that we are all one people--we just identify ourselves with certain countries, regions, languages, religions, groups, etc. We set up the boundaries much like fences built to keep our "kind" in and the "others" out. Sad, when you think of it that way.
#2 is correct in drawing attention to how the poem stresses the artificial divides that we as humans have built up between us and how these man-made barriers often make us forget the common, shared humanity that unites us all. In a sense the poem is arguing that it is forgetting this fact that makes so much cruelty, anger and suffering possible, for the existence of countries means that we define people from different countries as being "separate" and "different" to us, therefore making them lesser than us. This poem reminds us of the shared bonds that surpass such superficial, man-made constructs.
Most of the poem is telling you how this can be the case. It is telling you that countries are artificial. It is saying that in all the ways that matter, we are all the same. Look in the poem and you will see a number of ways in which we are the same in Kirkup's opinion.
For example, all people walk upon land -- the dirt is essentially the same -- and all people will end their lives by dying. All people, he says, want to love in the way that we want to. All people wake up by opening their eyes.
What he is saying is that in all the ways that really matter, people are all the same so the fact that we are from different countries does not (or should not) matter -- we are all the same.