I was going to post this the other day. Some of its already been covered but to re-edit will take as long as it took to write originally. Sorry if there is a little bit of repetition of some of the principles I've already advanced. They're probably explained a bit more in depth here though.
I disagree that the SSM proponents are trying to make marriage 'available to all'. They may dress the argument up as 'equality' but I'd have more respect for the principle they were putting forward if they championed the 'right' for people to marry 'whomever they like' as they often suggest. If it actually is 'marriage equality' then why not open it up to Muslims and let them marry 2-3 different wives or indeed anyone who is interested in a polygamous relationship. So I reject the proffered principle that the SSM debate is about 'equality'.
Of course, you will on occasion come across SSM proponents who actually do support extending the definition of marriage to include polygamous and other forms of marriage on the basis of 'equality'. I respect that they are least being intellectually honest when they discuss the principle of 'equality' but suspect that most Aussies would reject that proposition to fully embrace the principle of 'equality' and what it really means. Of course, another contributor has pointed out that the government does in fact prohibit certain relationships deeming them un suitable for marriage- sorry, can't remember who that was- so unless the SSM advocates are wanting to get rid of these restrictions also spare me the BS argument about #equalityforall.
I find it interesting that you say the issue of family is 'irrelevant' Le Pingouion. I think the research is pretty clear that family structure is important. Sure we have divorce (probably too much of it and I reckon an argument can be made that the ease of divorce has probably weakened the institution of marriage) but your line of thinking seems to be 'family structure is already so fractured that SSM fracturing it potentially more won't matter'. That's faulty logic. Heterosexual marriage is practised imperfectly so therefore SSM should be legislated so that it too can be imperfect? That's like when SSM proponents uphold Kim Kardashian getting married and divorced quickly as an example of why they should be allowed to marry. When some heterosexual people treat marriage as a convenience and a joke it doesn't automatically follow that SSM should be allowed because of the dumb things that heterosexual people do and gay people should be able to do that too. That's false logic and when Kim Kardahsian did what she did that weakened the concept of marriage for everyone. It cemented further in some people's minds that it's not an institution that is critically important for the make up of a society and most people who support traditional marriage are horrified at the way some people trash it.
In that respect I think that SSM proponents try and restrict the impact of SSM as not having an impact on my marriage and instead frame the argument around pro traditional marriage supporters as 'denying' someone else something- as we've seen in this thread. Reivelo and Le Pingouin believe they are not imposing anything on me when in fact they are- they're changing the definition of my marriage. They're putting forward the proposition that a mother and a father are irrelevant and the roles are interchangeable. Sure, some families do awesomely well without one or the other (and sometimes sadly both) but I suspect that deep down, most people would want a child to be brought up with the love and care of both their mother and father.