Opposition Leader Bill Shorten has declared the Prime Minister personally responsible for “every hurtful bit of filth” unleashed by the same-sex marriage plebiscite as he committed Labor to campaign for a ‘Yes’ vote.

In a fiery speech following Question Time, Mr Shorten ended uncertainty on whether the opposition would boycott the $122 million, ABS-led postal vote, which it has labelled a “waste of time”, saying that the “most powerful act of resistance and defiance is to vote yes for equality”.

Urging LGBTI Australians to take part in the process, he said: “I wouldn’t blame you if you just wanted to just chuck that in the bin. But let me say to you, that is what they want you to do.”

Mr Shorten also said the Prime Minister had “licensed” the debate, adding: “I hold you responsible for every hurtful bit of filth that this debate will unleash.”

Mr Shorten’s speech, which drew a standing ovation from the opposition benches, was followed by forceful contributions from pro-change Liberal MPs, including gay MP Tim Smith, who had briefly considered defying his party to support a free parliamentary vote on the issue.

Noting he had been engaged to his partner for seven years, Mr Smith said he just wanted the issue resolved.

“It’s frustrating to watch the moral posturing on the issue by many on the other side who have constantly delayed, stalled, blocked and opposed change before changing their opinion in favour – now with zeal,” he said.

“Respectfully, some of us have always had a consistent position, and taking a lecture about the failure to pass a change in the law from the opposition is a bit rich.”

Gay Liberal MP Tim Wilson says he wants the issue resolved. Photo: AAP

Mr Smith also rebuked former prime minister Tony Abbott, who on Wednesday said people should vote ‘no’ if they were “sick of political correctness”.

“My personal view is those arguments are laughable. The choice is not whether we engage or not,” he said.

“The choice is whether we allow these statements to go unresponded to. The choice is whether we stand up to those who want to keep us down. The choice is only to win.”

Liberal MP Sarah Henderson, who also supports change, said it was best “hateful words” from a small minority were not elevated.

“I will be the first to condemn hateful, vindictive, offensive words that are said in this debate,” she said.

“But can I make a very important suggestion … Please do not bring those hateful words, which might be watched by a small television audience of 3000 or 4000 Australians, into the national parliament.”

Labor had earlier used Question Time to ask Mr Turnbull about former Liberal MP Bronwyn Bishop’s suggestion on Sky News that same-sex marriage could lead to polygamy.

The Prime Minister confirmed that the government would not allow a free vote on the issue if a majority of Australians voted ‘no’ in the postal plebiscite.

“I encourage every Australian to exercise their right to vote on this matter,” he said.

Same-sex marriage opponents hit at out what they claimed they was biased media coverage and claimed a change in the law could lead to the persecution of Christians and other religious people.

“Even the ABC, who are tasked with being fair in their charter, haven’t actually been fair on this issue and haven’t equally given both sides an airing,” Liberal Senator Zed Seselja told Sky News.

The ABC issued a directive to staff hours later requesting that do not declare a public position on the issue or use the phrase “marriage equality” in their reporting.