I feel that if anything at all is to happen (e.g., constitutional amendment), a vote needs to be held. Just as it is mandatory in elections, everyone should be obligated to vote - that way, we can have a thorough and accurate representation of where the population stands on the issue. Everyone would be entitled to their own opinions, everyone would have an equal voice, and no politician could politicise the issue, which is simply morally and ethically egregious. We are a democracy after all.
My feeling is that if a change was to be made to the constitution to enable same sex couples to wed, then a very strict wording must be employed so as to prevent exploitation of the novel amendment. People will pursue any means to gain an advantage in this life, and if a legal document permits such behaviour, we would have people entering into all sorts of marriage arrangements for tax avoidance purposes, welfare, etc. Hence, whatever change is to be made must be considered with great thought. No changing of Facebook pictures will ever amount to anything significant in the way of change that betters society.
Peace.
P.S. I normally do not weigh in on these things, which is why I presented no view of my own on the matter.
Parliament is clearly given the power to legislate over matters relating to marriage in the Constitution (Section 51). This is why the ACT's same sex marriage law was overturned last year - it conflicted with federal legislation (Marriage Act.)
1 If Parliament wants to legislate SSM into law, all it takes is passing some legislation, as with anything else. It doesn't require a constitutional change. Although the pro-same sex marriage side would likely win (65-70% of Australians support same sex marriage) it the campaign would throw up some pretty disgusting bigotry - as what happened in Ireland, California. Calling for a plebiscite (or worse, a constitutional amendment) is just a politician's ploy to dodge confronting the issue. This issue is inherently political.
Nobody thinks that by changing their Facebook picture they'll radically transform society - but it's a harmless way of expressing solidarity with LGBTIQ+ individuals that they know. Tony Abbott won't change his opinion on SSM as a result of this, but plenty of younger LGBITQ+ individuals - particularly those still in the closet feel socially isolated, confused and alone. Seeing your Facebook newsfeed become a rainbow tells them that no, you're not alone, and yes, society does support you.
1. Yes, lurking lawyers, I know that the ACT's relationship with the Commonwealth is quite different to that between the Commonwealth and the states

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Yes. Incest is completely different to gay marriage. I think my opinion would change if it were perhaps second cousins or maybe cousins but brother and sister? That's wrong. And you'd have to work our where the lines are between abuse/emotional abuse and two people who love each other and want to marry. Because say one sibling was taken advantage of when they were younger or 'groomed' by an older sibling- that would be wrong. If two people wanted to get married and then found out they were siblings? That's different.
These things shouldn't even be compared.
Indeed. Power imbalance. Also worth pointing out that plenty of societies throughout history (including Western ones, surprisingly recently) have accepted same sex relationships, but the incest taboo is one of the most universal known in anthropology.
It's also worth pointing out that, in many ways, it's remarkable that we're even having a conversation about same sex marriage. Homosexuality was illegal in Tasmania and Queensland up until the 1990s (although not enforced,) and illegal and enforced in several US states until 2003. Recognition that homosexuals (and their relationships) deserve full, civil rights has happened remarkably quickly.