We do not accept that race, gender or religion should be the basis of discrimination. Tanya Plibersek makes the point that support for marriage equality should be seen in these terms. She reminds us that her political party, as a matter of principle, does not believe in discrimination before the law and so should, as a body, support the equal right of people to marry irrespective of gender. It is not, she argues, a matter of 'conscience', but one of principle.
It's difficult to argue with the logic.
Whether it's good politics or not is a different question. It might well inhibit the passage of any relevant legislation through the parliament. But maybe principles should come first.
Our evolutionary imperative is towards a more equal and pluralistic society. That grand sweep of human history is unstoppable, despite hiccups and short detours. It's clear that marriage equality is on a powerful wave traveling in that direction. Look at the world, especially those nations we like to compare ourselves with. The UK, Canada and NZ are now on the right side of history, Canada for a decade now. The USA is at a Supreme Court legislative tipping point, having already mostly made its choice to be on the side of equality.
How long is Australia willing to be out in the cold?