Plaintiffs attorney David Boies is about to begin his cross-examination of Proposition 8 witness David Blankenhorn, who has testified that allowing same-sex marriage would lead to the erosion of marriage.

Blankenhorn spent much of the past hour discussing the threat of the “deinstitutionalization” of marriage, essentially that its value would erode in society if gay and lesbian couples were permitted to marry. Blankenhorn said there already has been a watering down of the institution, with more children being born out of wedlock, conceding that heterosexuals have already begun the process. But he repeatedly suggested that same-sex marriage would doom the institution, disrupting the lives of children, discouraging people from marrying, producing divorce and leading eventually to quests to legalize other forms of marriage, including polygamy.

“If you change the definition of the thing, it is hard to imagine how it would have no impact on the thing,” Blankenhorn said of changing the scope of marriage.

The botton line for Blankenhorn: putting children with their biological parents is marriage’s “purpose in society.”

Read the rest of Howard Mintz’s San Jose Mercury article here.