Elaine Smith, a deputy presiding officer of the Scottish Parliament, appealed for an open debate as the Scottish Government prepared to bring forward the landmark bill next week.
It emerged yesterday that the Labour MSP for Coatbridge and Chryston told a recent meeting organised by Scotland for Marriage, the pressure group opposed to same-sex marriage, she would vote against the proposals.
At the meeting in her constituency she rejected the description of same-sex marriage as "equal marriage" and insisted she was not homophobic.
Since speaking out she said she had become a target, particularly on Twitter. She said: "I explained that I intended to vote against this bill in tune with the wishes of the majority of my constituents who have contacted me.
"I predicted that in speaking or voting against these proposals, I would undoubtedly be verbally attacked and labelled homophobic. That prediction seems to be coming depressingly true."
She added: "It is astonishing that a politician cannot represent the views of their constituents without being vilified and subjected to personal attacks.
"Speaking against the redefinition of marriage in modern Scotland, sadly, leads to verbal attacks which seem to be an attempt to try to shut down debate and intimidate opponents."
Ms Smith argued that existing civil partnerships ensured equality for gay and lesbian couples.
She acknowledged the "sincerely held beliefs" of the bill's supporters, but said gay marriage was an attempt to redefine the meaning of marriage as a union between a man and a woman.
She challenged supporters of same-sex marriage who have called for a calm debate to "make their rhetoric reality by confirming I am entitled to my view and, indeed, to represent the views of the majority of constituents who have contacted me".
So far only a handful of MSPs have declared their intention to vote against the bill, which is not expected to face a final vote until late next year. Ministers hope the first gay marriage ceremonies will take place early in 2015.
The Equality Network, which has co-ordinated the campaign for same-sex marriage, said the debate should remain respectful.
Director Tim Hopkins said: "Elaine Smith is entitled to her view, but she is wrong on the facts. A large majority of Scots, and an overwhelming majority of LGBT people, supports same-sex marriage. Those who want a same-sex marriage will be able to marry; those who don't won't have to, and no church will be required to do them. It's about freedom of choice for all."
He added: "This debate should be conducted in a respectful way – something we as an organisation have always done.
"We have not heard of any report of hate crime against people because they oppose equal marriage, but we would urge anyone who experiences any hate crime to report it to the police."
Health Secretary Alex Neil said last month the Marriage and Civil Partnership Bill will be published before MSPs begin their summer recess at the end of this month.
The move to allow same-sex marriage is opposed by the Kirk, the Roman Catholic Church and Muslim leaders, but it has the backing of the leaders of all the main parties at Holyrood.
Ministers say the bill will be designed to protect celebrants from having to conduct same-sex marriage services if they object.
The Equality Network is planning to release a new film, celebrating "love and equality", to coincide with the bill's publication.
Scotland for Marriage, meanwhile, said it will step up its cam-paign and encourage its supporters to write to about 50 MSPs asking them to vote against the bill.