It is instinctive to preserve or "save" life, as an extension it is natural to defend one's self, one's own family unit. Extending farther it is natural instinct to preserve and protect community and defend it from "suspicious" change i.e. anything different or foreign.
Of course this is based in ignorance and fear...but these, I can appreciate as natural instincts and based in survival.
It is also intrinsic to humans to notice any physical difference and as children do, to comment on differences, perhaps based in some logical survival-of-the-fittest-procreate-only-with-the elite instinct, or an instinct to herd together with one's own kind... "PC" approaches often focus on phasing this kind of thinking out.
However, the world is changing, it is no longer necessary to resolve disputes by beating the neighbouring tribe over the head with a dinosaur bone.
It is emerging, in my opinion, that multiculturalism benefits the human race and is the way we should be heading.
One example, the USA makes progress on the back of multicultural knowledge and abilities. People of every race and creed live in that country with comparatively few race issues. By that, I appreciate there are issues, but people are not engaged in inter-race physical war. Their diverse knowledge-base works together to achieve the aims of that country.
The UK also is multicultural and it is government policy to embrace that aspect of society. It used to be socially unacceptable to marry inter-racially. Times have changed. That is commonplace in many societies now.
Apart from my personal feelings that racism is a social injustice and it is abhorrent and ignorant etc, it makes sense to me on many levels to phase racism out. It makes no kind of sense to retain it. But I think this is an issue which will self-resolve over time. The world is getting smaller with technology. I have hope that we will evolve past racism.
I am not militant in support of anything, preferring to use routes established within the political system to challenge injustice. There is almost always a better way to make a point than violence.