Mathematically in the abstract, intermarriage is almost certainly a net gain for Jewish numbers. The offspring of all Jewish women who marry out are still deemed Jews. And so if even one Jewish man who marries out raises his children as Jews, that is a gain (whether or not the mother converts according to Orthodox specifications). Even the Orthodox ought to have a hard time arguing with these metrics. Of course the expected dilution of identity in an intermarriage and the drop off in participation in synagogues and yeshivas, sets off alarms for the Orthodox since it means fewer clients for these institutions.
Here is a blurb from the Times:
...the seemingly incandescent wedding of Ms. Clinton and Mr. Mezvinsky has churned up ambivalent reactions among the nation’s almost six million Jews.
There is a clannish pride that after a history of exclusion and prejudice, the grandson of a Jewish Ohio grocer could marry into what passes for political royalty in the United States.
But some Jews fear that the societal openness confirmed by high-profile intermarriages like that of Ms. Clinton and Mr. Mezvinsky, or Caroline Kennedy and Edwin A. Schlossberg in 1986, prod more Jews to marry out of their faith. That, they worry, could threaten the vitality of a group that represents no more than 2 percent of the American population.
In an editorial, The Forward, a liberal Jewish affairs newspaper, called the Clinton-Mezvinsky marriage “a milestone of sorts, a measure of social acceptance, a sign that we’ve arrived.”
But it took note of the conundrum: “This nuptial is also representative of an increasingly vexing challenge within American Jewish life because we know that — apart from the celebrity and the Secret Service — the Clinton-Mezvinsky union is fast becoming the new normal.”...