Who checks the yichus of each bochur in Lakewood and Ponevitch to make sure his grandparents are true Yidden?! Do the Rosh Yeshivas go back a few generations on the maternal side to make sure this talmid is a Yid? Who does this?!
What about mamzerim? If the grandparents remarried without a proper get, if there was an agunah that remarried (very common in pre-war days) without a hetter that we all accept, do you realize the michshol in shidduchim??
There might be 20-60% goyim or mamzerim learning in Bnei Brak! GEVALD!