Last Friday, Professor John Haldane, during his talk to the Iona Institute, stated that sexual relations in modern societies are now “governed by two principles; the principle of sexual attraction and the principle of sentiment”.

He said: “The argument that has evolved from that is very simple. It’s just this: that sexual attraction and love are the determinates of human happiness and should be consummated where sincerely and consensually felt.”

He said this could give you an argument for same-sex marriage, “but it will also give you an argument for polyamorous [multi-partner] marriage and it’ll give you an argument for incestuous marriage”.

In Canada, the Toronto District School Board seem to be eager to prove his point. It has launched a campaign in schools called ‘Love has no Gender’, with accompanying posters. Look closely at the poster in the top right of this blogand you’ll see ‘hearts’ containing not two, but three people.

The posters have been denounced as promoting polyamory.  However, a spokesperson for the school board says the images in question are not promoting polygamy, but “are designed to support an individual’s right to choose whom they love, regardless of gender”.

Spokesperson Ryan Bird said: “For example, the reason for depicting two women and one man was meant to show that a person can be attracted to more than one gender.” In other words, those who are bisexual.

Maybe so. But on what grounds could those behind this campaign deny the ‘right’ of a bisexual person to marry one person of each sex?

Once you allow that sexual love is all about sentiment and sexual attraction what is the argument against multi-partner marriage, let alone same-sex marriage?