On Tuesday night the House of Commons voted by 400 to 175 in favour of same-sex marriage. Interestingly, among the 175 who voted against were 22 Labour MPs.

This was unexpected in that Labour is committed to equality, and same-sex marriage is normally argued for in the name of equality. So why would 22 Labour MPs vote against same-sex marriage?

Scottish Labour MP Jim Dobbin explained why in one of the best speeches of the night. (The text of the speech can be found here (scroll down to find it) while a video of the speech can be found here.)

Mr Dobbin began by noting the truly radical nature of what the Coalition Government was proposing.

He then clearly set out the definition of marriage.

Marriage, he said: “is primarily an institution that supports the bearing and raising of children in a committed and constant relationship”.

He continued: “The traditional understanding of marriage has three basic elements: it is between a man and a woman, it is for life, and it is to the exclusion of all others.”

Crucially, Mr Dobbin went on to skewer the suggestion that traditional marriage somehow created inequality.

The crucial elements of marriage, he said “are designed not to exclude people or create inequality, but to promote the unique benefit of marriage in our society: it secures family environments and provides the essential qualities of safety and reliability for children.”

He added: “Worryingly, the Bill rarely mentions children or parenthood. It emphasises the decision to take part in a ceremony more than the commitment to a lifelong relationship or having children. It is as if those elements are of no consequence.”

Mr Dobbin then challenges the idea that same-sex marriage was about equality and fairness, terms much used by the bill’s supporters.

“The equality agenda has been narrowly limited to dogmatic principles of uniformity. Such language makes open debate and disagreement about the Bill look like prejudice,” he said.

He continued: “The Bill promotes the erroneous notion that ‘uniformity’ is a good definition of ‘equality’. Men and women do not have to be the same in order to be equal. Having the same experience does not make people more equal. We should be promoting equality, not uniformity, and be able to celebrate difference.

“This is not a Bill that has equality at its heart. In honesty, it is a Bill that dilutes the meaning of marriage.

“Holding a traditional view of marriage should not be seen as discriminatory. Unfortunately, the Bill has promoted that notion. It has not created tolerance, but has highlighted division. The Government cannot guarantee protection for Churches or individuals with a traditional view because they cannot predict or control what happens in the courts. What has happened to Catholic adoption agencies is a good example of that.

“Moreover, the Bill no longer promotes exclusiveness. It does not consider adultery to be a violation of commitment and so it undermines the nature of marriage and the way in which marriage promotes predictable, long-term family environments for children. That is a worrying move for a Government to make. Are the supporters of the Bill really saying that marriage is good for society, while at the same time reducing the substance and value of marriage?

“The Bill has many pitfalls. Changing the definition of an institution that has served society well is hasty and destructive. I cannot support such a move.”