For a rather different view of why Jews intermarry, I commend to your attention this essay by Zackary Sholem Berger.*

On the anecdotal, personal level:

My mother (Jewish) married my father (not Jewish) not because she's a crying spoiled baby and her parents didn't care what she did. She married him because he was her bashert--the right person for her--AND because he would join her in creating a Jewish family, even though he did not convert. (He practises no other religion, and Judaism has always been the only religion of the household: I'd say he is in many ways a good fit with the category of the ger toshav.)

I (Jewish) went out with and got engaged to my now-husband (not born Jewish) for much the same reasons. As it happened, his positive experiences with all that Jewish life and learning have to offer led him to become a ger tzedek and convert to Judaism in the year before our wedding--and in so doing completely changed and deepened my own Jewish life and practice. Certainly, I know many Jews by birth for whom their partner's decision to become a Jew by choice has done the same--but so do other important family events. (For my mother, it was saying kaddish daily for her father, who died when I was in high school: she became more involved in Jewish life years before I did).

Those who want to "fight intermarriage" might hail my story's outcome as another triumph for "in-marriage" now that it's between 2 Jews--but they fail to see the damage done by treating my supportive non-Jewish fiance as the enemy before showering him with love as a new (and newly-acceptable) Jew. In either case, he would have helped me build a bayit ne'eman b'yisrael, a faithful household in the Jewish community, whether or not both of us were Jews.

My story isn't everyone's story--but there are a lot of us out there. Recent Hillel surveys show nearly half of the Jewish students on campus have one Jewish parent. And these aren't all marginal Jews: I've known Hillel presidents, leaders of campus Jewish organizations, and other core, committed Jews who, like me, have one Jewish and one non-Jewish parent.

The question you should be asking, Destrudo et al., is what will bring more of those who do choose to make their lives with a non-Jewish partner--regardless of your disapproval--decide to make Jewish choices in how they live that life and create their household.

As for the obsession with numbers:
in my family it's all increase--
1 Jew (my mother) + 1 non-Jew (my father) = 3 Jews (me and my 2 brothers)
as a couple, we have:
1 Jew (my mother) + 3 non-Jews (my father and my husband's parents) = 2 Jews (me and my husband)... + any children we should be blessed with, who will be nice Jewish children with various beloved non-Jewish relatives. No identity crisis there!

When my extended family gathers for seder every year, there may be 2 non-Jewish spouses, 2 Jews by choice, and a bunch of born Jews at the table...but there's no one who's "married out." We're all in--whatever the religion of a spouse or parent. No children being raised "out of the faith," no one "lost" to us or to Judaism: so much for the siren call of dominant Christianity or areligious apathy. I know that statistically our family snapshot is not the nationwide norm--but I think it says a lot about the pull of a strong Jewish identity rooted in committed family life.

I'd rather focus on what we can do to let Jews and any non-Jewish partners and friends see all that Judaism has to offer them--and let as many Jews result from that as it may--than obsess about sheer quantity, or make grossly oversimplified generalizations about quality Jewish life being only possible with--or an inevitable outcome of (would that it were so!)--2 partners who are Jewish at the start of the relationship. Let's build up, rather than tear down. I'm ready!

*Two excerpts from this essay provide a valuable overall framework for understanding what else intermarriage might mean or be, consonant with but not limited to my own story:

What might be going on in the mind of the committed Jew when he or she finds "the right person" – who isn't a Jew? It's quite simple: he or she imagines a future married life which includes both involvement in Judaism and marriage to a non-Jew. According to his or her deliberations, a non-Jewish spouse does not compromise individual, Jewish aspirations.
...
With regard to the non-committed Jew, perhaps the foregoing discussion provides a productive approach: rather than "enticing" the marginal Jew with dire predictions of the downfall of the Jewish people brought about by intermarriage, we can provide positive examples of substantive Jewish life among individuals from a variety of backgrounds and individual choices. All of these Jews, together with their families, make up the Jewish people, which is strong and broad enough to share its bounty with the "chosen non-Jews."