Some people believe only male-female marriages should be allowed for their traditional purpose of helping and encouraging couples to raise children properly.
Some people believe that any 2 people should be able to marry and that gender is irrelevant since if they are responsible 2 men or 2 women can raise children and deserve the same rights as heterosexual couples.
Some people believe that only same-gender couples should be allowed to marry, it's a big country.
So far we have supporters for sexual-specific marriage laws, sexual-unspecific marriage laws, so one last opinion remains.
No marriage laws!
This is the correct opinion, people should be free to make deals they want and they can call it the marriage between Mr/Ms A and Mr/Ms B, however there is no reason to have special laws giving people tax breaks or whatever for marrying.