A lot of the time it is a question of whether the Governement is trying to impose their morality onto the legal system. Big example:
R v Wilson - Heterosexual married couple. Husband brands his initials onto his
backside. They split up, she takes him to court claiming she didn't
give consent for this at the time. She needs medical attention. Court
holds that the husband has done nothing wrong.
R v Brown - I group of consenting heterosexual men, caught performing s&m
sex acts on each other (e.g. whipping etc.) taken to court by the state
and, even though none of the men involved required any medical
attention, all held guilty for GBH.
People working within the Governement are described as middle-minded for a reason. There is no cross-section and I think it's fair to say that those working to lead are country, in reality, know and understand very little to nothing about us, and yet it's their views and their reasoning the we must follow? Not fair! Plus, not allowing two people to do something because of their sexual orientation is the exact kind of discrimination that Governments are supposedly 'working against'.
The Government should stay out of gay marriages as much as they stay out of everyone elses.