We have reached a fair degree of agreement here.
I believe we agree that American culture, that powerful amalgam of so many ingredients, will overcome any ethnic identity in a few brief generations. Thus Chinese, Jewish, or any other ethnic identity is doomed--or at least likely to be reduced to pale remnants of once-vibrant experiences. I believe we agree this is not to be regretted, for it is how we all become Americans.
Where religion fits in all this is the remaining question, and it is a very large one--at least for Jews. If we define "Chineseness" as a form of ethnicity, it will be kept alive by immigration but will and should decline. The same would and will be true of "Jewishness," unless it has a religious core. What you write about your Jewish friends is unsurprising, if tragic. Polls show time after time that most Jews define their Jewishness in secular terms, and it is therefore silly to think they won't intermarry. But how many are "they"? You suggest that only "relatively few" Jews have much devotion to their faith, but perhaps the numbers are greater and perhaps they are growing. One likely prediction for the Jewish future here in America is polarization: many Jews leaving the community through intermarriage, but leaving behind a smaller core that is more religiously oriented. Today's 5.5 million Jews may, in two generations, be reduced to 3 million, but those 3 million may cling much more tightly to their faith.
Those future generations are, of course, the children of whom you write. And here our visions differ. You write of the "receptiveness of the child" as if that were a truly independent variable, while I would think that it is a largely dependent variable--hence the data suggesting that kids who go to Jewish day schools and whose parents take them to synagogue are far more likely to resist intermarriage. You also write of the "undiscovered world of our children" as if it were to be created from whole cloth. To a Jew, that's all wrong. Our children are not unguided missiles whom we launch; they are born into a covenant and are meant to be raised and educated to stay in it, continuing the chain that began with Abraham. Your formulation is very modern and very American, but the Jewish view is different: American culture today speaks of rights, while the Torah speaks of duties. You know the point I'm making, and you have indeed made it. What I am saying is that Jews are not free to "leave things alone," in your wonderful quote from Chesterton.
Perhaps this is the key to the intermarriage question. Do you see your children as free agents roaming around in American culture, or do you see them as having prior commitments? Any Jew who answers, as American culture does these days, that autonomy is the highest possible value, is answering that intermarriage is fine and that being a Jew is really like choosing a hobby. Make it, unmake it, forget it, what's the big deal. Judaism demands more, and perhaps you and I are back where we started. Ethnic intermarriage is as American as apple pie. Where you stand on religious intermarriage depends on where you sit, especially on Saturday or Sunday morning: in a pew, or not.