In my country the checkbox must be for opt-in. And it must start off unchecked.

Not in Australia, but good suggestion in some other countries!

I see the block of the birth certificates as being ostensibly in support of the prohibition of this practice, but I can also very well see the underlying intent as being anti- same-sex-parenting.

Further, I don’t understand why the practice should be prohibited in the first place.

So I disagree with it, but on the other hand I also disagree with it. Am just a filthy foreigner though so other than this comment I’ll keep it to myself.