New Zealand Votes for Equality.

I seriously don't get what's SOOO important about marriage...
Other then religious stuff...

What Miek and Sapta said above is true, but if you're talking about why people still place importance on marriage, it did have a lot of social value in the past and the couple being of the opposite sex did matter since it ensured continued survival. With the current advances in technology and changing values marriage's importance has been diminished by a lot, especially as one could more easily raise kids alone than they could in the past.

In other words, as marriage does carry with it certain implications, obligations and rights it is only fair that same-sex marriages are allowed so that they receive the same rights.