In decades past, South Australia built a reputation as a leader on social reform.

It was the first state to give women the right to vote and stand for parliament, and under the leadership of Don Dunstan, was the first to decriminalise homosexual acts.

Some of the most public campaigns in recent times are for law change on a trio of thorny issues: the decriminalisation of sex work, abortion law reform, and voluntary euthanasia.

In an interesting turn of events, campaigners were hoping the election of a moderate Liberal State Government last year would help their cause, after years of failed attempts under the former Labor government.

On sex work, advocates got further than ever this year, at least until last fortnight when it was defeated in Parliament.

The Lower House — which had never considered the issue before — rejected the bill at the first opportunity.

Premier Steven Marshall had thrown his support behind the bill, saying it was an issue some other states had dealt with "decades and decades ago".

Sex workers Dame Catherine Healy (far left) and Julie Bates AO (far right) with Liberal MLC Michelle Lensink, Greens MLC Tammy Franks and Sex Industry Network president Roxana Klara at Parliament. ( ABC News: Rebecca Puddy )

Deputy Premier and Attorney-General Vickie Chapman described the result of the vote as "disappointing".

"I feel for those sex workers in our community who will still be treated as second-class citizens, and will still be able to be prosecuted for their work," she said.

"With the failing of this bill, sex workers are now still left in a position where their safety is at risk."

But there were conservative Liberals who had a different view.

South Australian Attorney-General Vickie Chapman spoke in favour of the sex work decriminalisation bill in SA Parliament. ( ABC News )

Liberal MLC Dennis Hood strongly opposed the bill.

"The left always seems to go for the most radical form of legislation that they possibly can," Mr Hood said.

"[It] was just beyond what I think most reasonable members would consider desirable for their electorates."

A group of socially progressive MPs across parties have been working together to advance all three social issues, and the sex work reform result threw up questions about whether abortion and euthanasia were also on shaky ground.

Next month, the state's Attorney-General Vickie Chapman will present a proposal for the full decriminalisation of abortion, and a parliamentary committee is currently looking at the issue of voluntary euthanasia.

Both issues are set to come before Parliament as a conscience vote, where MPs will not be bound to their party's position.

Lower House 'does not fully understand' debate, suggests Greens MLC

Advocates had expected the sex work vote to be close.

Several sources have told the ABC that at least one MP indicated support and then voted the other way.

South Australian Parliament's Lower House voting on the sex work decriminalisation bill. ( ABC News )

SA Greens MLC Tammy Franks first introduced this year's bill to Parliament, and said Lower House MPs had a "much shallower level of understanding of the debate", because they had not been through the same extended parliamentary committee process as the Upper House.

She said other barriers were objections raised by councils and SA Police, the latter called for protections to prevent organised crime moving into the sex industry.

"We saw what is being called an unprecedented entry into the public sphere by the Police Commissioner Grant Stevens," Ms Franks said.

Will the vote impact further reforms?

The staunchest opponents of the sex work bill could well oppose changes to abortion and euthanasia laws.

However, one member of Labor's left faction told the ABC it was unlikely that all MPs would split along the same lines.

They said they thought abortion law reform would have an easier path through Parliament, but feared euthanasia would be less likely to succeed than they had initially thought.

The vast majority of Labor's right faction, including Opposition Leader Peter Malinauskas, voted against the sex work bill.

Tammy Franks claims MPs don't fully understand the sex work debate. ( Facebook )

But it is unclear whether those MPs will view abortion and euthanasia bills as less extreme than the proposed model to decriminalise sex work.

Dennis Hood said it would come down to the specifics of any legislation.

"There is some reform in the legalisation of prostitution that even a fairly solid conservative like myself would look at and consider," he said.

"I don't think these things are set in stone except for the hard left, they'll always I think support social change."

Tammy Franks said the parliamentary battle over sex work was always going to be the hardest to win, and some MPs told her they didn't want to expend political capital on that issue.

"There were people who said 'Oh, look, I can't vote for sex work because I'm voting for abortion'," she said.

"Quite a few people are in that camp."