And so another domino falls. A vote in the National Assembly overnight made France the 14th country to legalise same-sex marriage, hot on the heels of number 13, New Zealand, last week.

The media were able, not quite accurately, to portray New Zealand’s vote as a matter of cross-party consensus. No such opportunity in France, where it was largely a party-line vote: those in favor were almost all from the government, and those against almost all from the opposition. A handful crossed over either way, but the margin of 331 to 225 was very close to the left’s overall majority of 340-226.

(The National Assembly website is extremely helpful, giving a breakdown of voting on the bill by parliamentary group – well worth a look, even if your French is only rudimentary. It’s something other parliaments should emulate. Despite such assistance, the BBC again managed to get it wrong, giving the vote in favor as 321, not 331.)

Same-sex marriage has been a divisive issue in France for some months now, with massive demonstrations against the bill. It contrasts with the generally positive atmosphere in New Zealand, and has led some commentators to wonder what it is about France that makes it different. As Fairfax’s Nick Miller said yesterday, “New Zealand’s parliament famously sang with joy. In France’s last week, MPs threw punches at each other at the end of a long and acrimonious debate.”

To my mind, this is one of those questions that it’s not necessary to overthink. Instead of having recourse to the mysterious power of France’s ancient but long-dormant Catholicism, I’d point to two explanations on the surface.

First, France (and especially Paris) simply has a culture of mass protest unlike most other countries. It was sanctified by the revolution, but it probably goes back at least as far as the “day of the barricades” in 1588. Public policy is repeatedly held hostage by demonstrations, as for example in the 2006 struggle over youth unemployment.

But the second factor is the politics: New Zealand had a large measure of consensus because same-sex marriage was proposed under a conservative government, supported largely by the left. In France, it was an official measure of a centre-left government. Its centre-right opposition opposed it, not because it had a strong ideological position, but because that’s what oppositions do.

The partisan nature of the debate encouraged (and in turn was encouraged by) the mass protests, but that doesn’t mean that the opposition UMP is fundamentally any different from its Australian or New Zealand counterparts. Its leaders are happy to collect votes from the extremists in the street, but the chance that they will reverse the measure when they return to government is negligible.