On the plebiscite/postal survey though: the government in Australia isn't bound by the results of it. It's just a survey. The fact that the Liberal Party put the result into law[0] within 48 hours is their own doing, submitted by an LGBT member of the party no less.
A conservative party would fundamentally not do this.
You can scroll down in the linked Wikipedia article to see how everyone voted. You won't exactly see significant, genuine opposition. There was arguably more opposition from the left-leaning alternative, the Australian Labor Party, that had the most people abstain in the senate.
[0] https://en.wikipedia.org/wiki/Marriage_Amendment_(Definition...