Avoid adultery and mamzerim by not having a religious marriage

Igros Moshe (E.H. 3:6) Concerning a couple who are viewed as being married. They claim that they were married in a civil ceremony in Communist Russia and then they moved to Argentina where they separated by civil divorce and she later married a second time in a civil service  and gave birth to a son who now wants to marry a Jewish girl. The question is the validity of the first marriage? It is clear that in those days in Russia there was very strong government pressure not to be married in a religious ceremony and clearly most people did not have a religious marriage but only a civil registration that they were husband and wife …. There were also rabbis who refrained from performing religious marriages because it was difficult to find a mikve since in most communities the mikve was either locked up or destroyed and only a few functioning mikves existed. Additionally it was common that eventually the couple would decide to separate, which in Russia was not done through a court but they simply separated and got remarried and if there had been kiddushin and she had the halachic status of a married woman this would result in producing mamzerim.  Therefore they advised parents not to pressure their children to have a religious marriage even secretly if it wasn’t clear they were observant Jews and that is also how I conducted myself. Consequently in those days in Russia a couple living together as husband and wife even for a long time can not be assumed to have the halachic status of being married. Only by means of a religious ceremony do they become married. This is also true for America for those who have a civil marriage or a reform marriage. But this is in regard to the sin of adultery and capital punishment but not regarding the prohibition of remarriage without a get. So it is always best to require a get even from  a civil marriage. In contrast Rav Henkin was very strict and considered civil marriage as marriage.