sam2 who wrote “Akuperma: It’s a dead dispute. The world holds like R’ Moshe. “
Many of the Religious Zionists, in Israel, in fact hold that marriages involving non-Orthodox Jews are valid, which is why they are so insistent that the Israeli government closely regulate marriage and divorce (a “frummer” approach is to follow R. Moshe and say that only frum Jews can possibly have the intent to be married “kdas Moshe v’Yisrael” and therefore there is no danger of the Am Ha-Artsim being safek mamzerim). Note that many new Baalos tsuevahos who were either married or “in relationships” before becoming frum do try to get a “get” to be certain, though since we are several generations into the “sexual revolution” the damage is done (if you have a “makel” attitude as to getting married).