It might seem obvious that the people who would be most eager to have their say in the upcoming postal vote on same-sex marriage would be those who want the law to change — same-sex marriage campaigners.

And that's largely true. Many of them are calling for young people in particular to get their names on the electoral rolls so they can send a clear message to Parliament.

But others are boycotting the vote altogether, and key lobby group Australian Marriage Equality hasn't clarified its own position.

Firstly, SSM campaigners across the board haven't changed their mind about a plebiscite

These are some of their reasons for opposing it in the first place:

They say Parliament is shirking its responsibility for making this decision

They say Parliament is shirking its responsibility for making this decision They say it's a waste of money because opinion polls already show most Australians support same-sex marriage

They say it's a waste of money because opinion polls already show most Australians support same-sex marriage They say the vote will be unscientific and there are worries there could be barriers to people having their say (for instance, unfamiliarity with the postal system among younger Australians)

They say the vote will be unscientific and there are worries there could be barriers to people having their say (for instance, unfamiliarity with the postal system among younger Australians) They say the negative campaign against same-sex marriage will be harmful for LGBTI people

None of these objections have disappeared, and same-sex marriage supporters hope a constitutional challenge stops the vote in its tracks.

But if the vote happens — and the Coalition Government is pushing ahead — there's debate about how to proceed.

Same-sex marriage advocate Rodney Croome says a poll of 5,000 people found 15 per cent of the LBGTI community support a boycott, while more than half want a campaign for yes.

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Some are boycotting because they don't want to legitimise what they see as an illegitimate vote

Former High Court judge Michael Kirby had initially been among those declaring they would boycott the postal ballot.

However he has since said he would vote in the survey.

"If there is no court challenge or no successful court challenge and if the government members don't come to their senses and terminate this very bad precedent for our governance, then I will myself be certainly voting yes in the vote," he said on Thursday.

For Mr Kirby, it's a personal issue. He's been in a relationship with his male partner, Johan van Vloten, for 50 years.

He had earlier called the decision to hold a postal vote "complete political improvisation".

"This isn't a plebiscite now, it's a completely novel, voluntary, non-binding, non-compulsory vote of a few citizens," he had said earlier in the week.

"It's something we've never done in our constitutional arrangements. It really is unacceptable."

Australians overall support a voluntary postal vote, with 43 per cent in favour and 38 per cent against according to an Essential poll published this week.

Others say boycott plays into hands of 'no' vote

The fear is a partial boycott would suppress the "yes" vote and get "no" over the line, so bolstering the case for leaving Australia's marriage laws as they are:

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The people making this argument want to make the most of what they see as a bad situation.

Prime Minister Malcolm Turnbull has urged people not to boycott:

"I encourage every Australian to exercise their right to vote on this matter."

Liberal backbencher Andrew Laming said talk of a boycott "is an indication clearly that the yes campaign feel that they cannot win a public vote".

Whatever happens, this isn't make or break for same-sex marriage

The Prime Minister says he won't be facilitating a free vote in Parliament on same-sex marriage should the ballot come back with a "no".

But earlier this week, Coalition MP Warren Entsch said "if it comes back 'no', I reserve my right as a Liberal to call on a vote".

That means there's still a possible path to legalising same-sex marriage this year even if the "yes" vote doesn't win.

And if same-sex marriage is defeated in this Parliament, Labor says it would legalise it should it win the next federal election.