Allowing gay couples to marry would undermine a "treasured institution", says Canterbury and Whitstable MP Julian Brazier.
The married father-of-three was speaking as the government launched a 12-week consultation on whether to allow same sex marriage in England and Wales.
Mr Brazier, who is a practising Roman Catholic, says he is opposed to the concept and given the chance will vote against it in the House of Commons.
He said: "It seems to me this is a very radical measure which will undermine a treasured institution and could have unforeseen consequences.
"We shouldn’t allow an institution of this importance to be re-defined simply to meet a rights agenda.
"It’s always been defined in a practical way which is quite restrictive when you think about it – there’s got be one of each sex, you can’t be related, you can’t be married to somebody else.
"If we start to deconstruct it at what point do we stop?"
He said: "I can’t see any logic as to why we should redefine marriage for the needs of one group of people and not others?
The proposed legislation - promoted by the Minister for Equality Lynn Featherstone - would allow same-sex couples to marry in a register office or other civil ceremony, but would still bar them from marrying in a religious service.
Andrew Brettell, a founder member of LGBT group Pride in Canterbury, said: "I am happy in my civil partnership. We do not want a 'marriage’, but there are those in the LGBT community who do.
"At Pride in Canterbury we want equality for LGBTs and indeed all people."
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