Gay partnerships

The quote below comes from a US site debating gay partnerships. I'm not going to link it as it is supposedly religion based but I think the overall tone is rabid. The quote is part of a comment. I take the poster's (a woman if you need to know) point and see it as something I'll try and remember for next time someone who knows me not seeks my opinion on the matter. So - what was it? Here you go...

Some people involved in the debate are concerned about the "slippery slope" idea. Marriage should be about love, but it's original intention was as a sort of "blessing" so that people could go on to have children, and provide them with a stable household. It's foundation is in procreation. When you redefine the concept of marriage to allow homosexuals to marry, all of a sudden there are countless other examples which arise. A father and daughter, for example. Or a threesome. Or sisters. The lines which currently surround the marriage concept blur.