(And probably anthropology thrown in there as well).

I don't get it, for people who claim to be super-rational, and only believing in "evidence", some of you atheists are a strangely illogical bunch.

And then when you say "Err...but wait, did you actually think this through - what about X?", they start throwing around labels like BIGOT, BIGOT!!!! NYAH NYAH!!!

Ok, I'll try and put in in HN tl'dr terms =).

Man + Woman = Procreation

That is a fact of life (literally, the fact of life) - human's engage in sexual reproduction.

For most of recorded human civilisation, we've had marriages - to try and foster the family unit, and engage in aforesaid procreation.

Now, in modern times, we've had an upsurge in homosexual relationships - some people decide to have sexual partnerships with same-gendered people.

Now, this can't by definition by procreative - which for most of recorded history was the point of marriage and families.

So some parts of society want them to come up with a new term to describe this relationship, which is sexual in nature, but not about families or procreation.

However, the other group say that because their relationships are sexual in nature, and they still like the concept of kids, they should still use the same label.