Phil and Pearl

http://www.telegraph.co.uk/news/newstopics/howaboutthat/7662232/Grandmother-and-grandson-to-have-child-together.html

The story linked to above might or might not prove to be for real. But even if it turns out to be an early April Fool's joke, it provides an interesting exam question for courses in ethics and public policy, constitutional interpretation, and civil liberties. I understand how the questions below would be answered from the point of view that is these days labeled "conservative."  I'm curious about how they would be answered from the liberal point of view.  Any liberal MoJ colleagues like to have some fun giving it a try?

"If Phil and Pearl [the grandmother and grandson in the Daily Telegraph story] would like to get married in order to bring up their child in the marital context, shouldn't they be permitted to?  If there are laws forbidding them from marrying or barring the legal recognition of their marriage, don't those laws violate their rights to liberty and equality?  Why shouldn't law honor all families, including incestuous ones? Is it right for law to impose upon people like Phil and Pearl (and Columbia professor David Epstein and his adult daughter: http://www.dailymail.co.uk/news/article-1339108/David-Epstein-Homosexuals-want-INCEST-different.html) majoritarian moral values they do not share?  Isn't opposition to love and its sexual expression by closely related adults simply rooted in disgust, prejudice, and animus?  Where are the studies showing that children raised in the homes of incestous adults in consensual relationships fare worse than others?  Aren't Phil and Pearl (and the Epsteins) just like other couples whose relationships we honor and are happy to recognize as marital?  After all, they have a relationship of mutual caring and sexual-romantic companionship and domestic partnership. They love each other and are willing to care for each other and take responsibility for each other.  Phil is Pearl's NOP (Number One Person); and Pearl is Phil's. If they wish to marry, how would their marriage harm yours or anyone else's? What justification could there be for denying them the right to marry?"