It was religion alone that helped Jews to survive especially in Europe for 2000 yrs. If Jews lose faith, they are also leaving their Jewish culture and identity behind. If Jews of Europe and Middle East had converted to Christianity or Islam in the past(and it was not that hard, considering the amount of persecution they faced), there would have been no Jew in the present.
The grandchildren or great grandchildren of these young secular Jews would not even know they had any Jewish(ness?) in them.
And as evidence, I am quoting from
A Portrait of Jewish Americans | Pew Research Center's Religion & Public Life Project