Apples & oranges.
You understand the reason why the right is not given, is because of what marriage is by definition.
Those who don't agree with the 'yes' vote, do not buy in the idea that somehow marriage is a right just for two people who love each other, but is instrically tied up with the raising of children.
for e.g.
https://www.facebook.com/VoteNoAustralia/videos/902321679922044/
correct, and neither do I think that is a good reason to vote yes/no
correction, not by convention, by definition.
The whole reason the state got involved with marriage was its connections with procreation and the responsibility of parents/raising children, it was/has never been about love, and the affirmation of love. Gay couples can have their approval by society and more, in the parades they run, they can be viewed as even superior relationships than the heterosexual relationships.