The WALL!

Nopes!
I am not talking about Rahul Dravid.
He used to stand like a wall between ball and stump(without even getting LBW :P)

But we all are standing between two groups of people. Thats racism.
India is a place, where racism shows up maximum possible variety.
We have racism based on cast, religion, language, state, sex and what not!

I tried to think a bit about the basic thought behind racism.
In general, we feel affection for someone who talks the same language. You can communicate to him easily and you can enjoy talking in your mothertounge!
While being out of station, you might find a person from your city close to heart, for you share the same background. You tend have some common memories, thoughts and something common to talk about. Certainly, you will have more belongingness with such person.
In such case, you'll tend to favour him against a person from completely different background.
This, I believe is the root of racism. (Thats why Marathi ppl grab most AAs in workshop :P.)
Jokes apart. When a person from different state/nation grabs an opportunity you would have otherwise got, you'll be hurt for sure.
This has lead to all the aggressive racism, from MNS to curry bashing.

Still the ideology is that its bad to have proud of your caste/religion and hatred for others.
But its still a great thing if you are proud of your country and hate other say Pakistan.
All the political tensions between two countries arrive mainly due to heads of the respective country. A soldier has no hard feelings for the opponent he is killing. And if they are, I believe that human beings are no different from wild animals.

To say in a a bit IITians fashion(Or call it the sheldon way), all people wanting peace, is a unstable equilibrium.
And racism is a basic instinct of man, which will not let the equilibrium to be achieved.