A Conservative cabinet minister has criticised the government time spent debating same-sex marriage.
Defence Secretary Philip Hammond said that the policy had angered many adding: "I have just never felt that this is what we should be focusing on."
But Tory MP Nick Herbert said polls suggested most people favoured reform and losing touch with young voters would hurt the party.
The proposals for England and Wales will be debated by MPs on Monday.
The Marriage (Same Sex Couples) Bill has split the Conservative Party but Prime Minister David Cameron and close colleagues are strongly in favour, as are Nick Clegg and Ed Miliband.
'Sense of anger'
When MPs were given a "free vote" on the issue in February nearly half of all Conservative MPs opposed it.
Mr Hammond, who has been open about his opposition to same-sex marriage, told BBC One's Question Time: "This change does redefine marriage. For millions and millions of people who are married, the meaning of marriage changes.
"There is a real sense of anger among many people who are married that any government thinks it has the ability to change the definition of an institution like marriage."
The introduction of civil partnerships in 2005 had dealt with the "very real disadvantage" that same-sex couples faced in the past, he argued. "There was no huge demand for this [same-sex marriage] and we didn't need to spend a lot of Parliamentary time and upset vast numbers of people in order to do this."
But Conservative Mr Herbert, a gay former minister, wrote on the ConservativeHome website: "How, precisely, would the the wedding of two people of the same sex in Weybridge change or devalue Philip Hammond's own marriage?"
Campaign group the Coalition for Marriage has collected more than 600,000 signatures calling for the coalition to drop its same-sex marriage proposals.
But Mr Herbert said opinion polls suggested the majority of the public were in favour the plans.
"Across much of the western world, the tide of change on equal marriage is running astonishingly rapidly, because public attitudes to gay people are changing at the same rate. Younger people can't understand what all the fuss is about," he said.
"I am sorry that it has caused disagreement in our party, but just as civil partnerships were opposed at the time yet became widely accepted very quickly, so I believe will gay marriage. Losing touch with the new generation of our electorate would produce a different and far more dangerous kind of pain."
Civil partnerships review
Mr Clegg responded to the debate on Twitter: "We're all different but our love is the same. Everyone deserves to live free from discrimination and prejudice."
Shadow home office minister Chris Bryant, whose civil partnership in 2010 was the first to be held in the Palace of Westminster, told Question Time he had always felt "slightly upset" when people said moves towards same-sex legislation would undermine marriage.
But he said the legislation should also allow heterosexual couples to have a civil partnership: "I think we should just have both for everybody. It should be exactly the same for everybody."
It has emerged ministers have tabled an amendment which would allow for a review of civil partnerships in 2019 at the earliest - five years after same-sex marriage is set to become legal under government proposals.
'Get on with it'
The review would pave the way for partnerships to be extended, or, if demand has plummeted, scrapped altogether.
Culture Secretary Maria Miller said the government was now offering MPs "the opportunity to have a review of this area, rather than legislating now without the required evidence".
She has warned that extending civil partnerships to heterosexual couples now would mean major delays to the introduction of same-sex marriage.
But gay rights campaigner Peter Tatchell said the public had supported the move in a consultation last year and ministers should "stop delaying and making excuses".
And Conservative MP Tim Loughton, who has tabled his own amendment calling for the immediate introduction of heterosexual civil partnerships, told BBC Radio 4's Today programme: "Let's get on with it, rather than let it drag on and on."
The former children's minister, who opposes same-sex marriage, denied that his amendment was an attempt to wreck the bill.
Meanwhile, crossbench peer Lord Dear has said he will table a motion opposing the Second Reading of the Bill in the Lords on 3 June, arguing that the government is pushing the legislation through without a mandate, as same-sex marriage was not in any of the main parties' manifestos.