If marriage can be redefined so that it no longer means a man and a woman but two men or two women, why stop there? Why not allow three men or a woman and two men to constitute a marriage?

Keith O’Brien’s quote reflects his opposition to the redefinition of marriage to include same-sex couples. He argues that if marriage is no longer defined as a union between a man and a woman, and can be expanded to include two men or two women, it opens the door for further redefinitions. By asking why not extend this redefinition to include more complex relationships—such as three men or a combination of multiple individuals—he is challenging the idea of changing the traditional definition of marriage.

O’Brien’s statement suggests a slippery slope argument, where he fears that redefining marriage to include same-sex couples will inevitably lead to the acceptance of other non-traditional relationship structures. This line of reasoning is often used by those who are against the expansion of marriage rights, as they believe that changing the definition could lead to further complications and a breakdown of established societal norms.

The quote also reveals O’Brien's concern with maintaining the traditional view of marriage, where the union between a man and a woman is seen as the only legitimate form of marriage. By questioning where to draw the line, he implies that altering the definition of marriage could lead to a loss of clarity and stability in the institution itself, potentially undermining its long-established purpose in society.

Ultimately, O’Brien’s words reflect a view held by those who believe that redefining marriage would erode traditional values. The quote uses hyperbole to suggest that expanding the concept of marriage to include same-sex couples could lead to even further changes that, in his view, might be difficult to justify or manage.