Okay, firstly, we obviously want all of these got rid of eventually, but we'll probably just have to wait for the singularity for that.
In the meantime, i think we need to recognise that they are separate things; there may be correlations between them, but this is simply a result of historical contingency, not a property of the things themselves.
Race is biological. It's a pretty random collection of genetic factors which relate to environmental and random factors in the place where your ancestors evolved. It's pretty much irrelevant for all purposes. Well, almost - there is one quirk, which i'll come back to.
Nationality is administrative. It's based on where you were born, the laws of various countries, and various ritual acts (immigration, naturalisation, marriage, etc) you have performed since. It's frightfully important administratively, but not in any other way.
Religion is personal. It's about what set of irrational beliefs you subscribe to - god died for our sins, there is no god but god, god does not exist. Religion affects your relationship with various imaginary superheroes in the sky, but in practical terms, it's irrelevant; it's purely internal, nothing to do with your interactions with other people.
Culture is everything. Culture is about morals, norms, social organisation, etc. Culture is fundamental to the way people relate to other people.
Discriminating between races is stupid and wrong; we call it racism. Discriminating between nations is stupid and wrong; we call it nationalism. Discriminating between religions is stupid and wrong; we don't actually have a terribly good word for it, although 'bigotry' is roughly right. Discriminating between cultures is necessary and right; it's different from the others because it affects how people behave towards other people, and therefore has the potential to conflict with human rights. We have to recognise that some cultural elements, and therefore some cultures, are less than acceptable.
And don't start with that cultural relativism bullshit. Human rights are absolute; that's an axiom where i come from.
A consequence of this is that multiculturalism is wrong; multiculturalism would have us accept that girls should be circumcised, thieves should have their hands cut off [suspect this is an urban myth -- ed.], marriages should be decided by parents [this too] and boys shouldn't cry. Wrong. What we need is to eliminate the bad elements, and hold on to the good: we should be working towards a single, optimum culture for everyone, based on rationality, equality and humanity; 'anaculturalism', if you will.
Another consequence is that we need to stop bashing Islam and Muslims. I think everyone with half a brain knows this, which is good.
Oh yes, the race quirk, which is in fact a general quirk: the reason why these four theoretically orthogonal factors are correlated in real life is to do with sex. People tend (and it is only a tendency) to be attracted to people from the same race, nationality, religion and culture as themselves, and of course are mostly going to be exposed to that sort of people anyway, and they're going to end up having sex, and so, children, with that sort of people. Since race, religion and culture do tend to be passed down in families, this leads to effective segregation along race/religion/culture lines, even within a single nation. Sucks.
Incidentally, Polly Toynbee's article 'Why Trevor is right' prompted me to jot this down.