“jdf, think western europe and USA where assimilation was in mid 1800 already.”
Yeah, but so what? If they assimilated, they assimilated. That means they aren’t going around identifying as Jewish nowadays. This idea that you’ll have a family line falsely identifying as Jewish, remaining secular all the while for 200 years is just implausible. At some point, they’ll just start identifying (correctly) as goyish or as nothing. It usually only takes 1 or 2 generations for that you happen, so nobody has to look back centuries.
“you didn’t know anyone with intermarried parents until you reached college in another state………………………….
I have no idea how old you are. I might guess your home state is NY”
Why is this hard to believe? If he grew up in a frum community, there’s no reason he would have met anyone “half Jewish.” Then he went off to college and met “the others…”