Wolf, I’ve got your back on this one.
I personally know many non-Orthodox Jews, including Conservative, Reform, and unaffiliated. Many are married to non-Jews. None were raised in Orthodox homes. As far as I can tell, they are continuing to practice the same brand of Judaism that they were raised in.
Are they shomer Torah u’mitzvos? Not a one. And with the exception of the Conservatives, they know it. One of the Reform jews I know introduced us once to a non jewish person and said, “We’re both Jewish, but ‘squeak’ is a real jew”. (Note: not that I agree with the implications of the words “real jew”; he’s as real and as jewish as I am, but what he meant was obvious to both of us.) The unaffiliated ones are comfortable with knowing (and asking) about any and everything, and doing nothing. Because that is how they were raised.
OTOH, when I’m speaking to the Conservative, he speaks with the sense of being on the same plane, religiously, with me. Whether it’s about a Succah, Torah reading, Bar Mitzva, wedding (chupa)- his perspective is that our ceremonies may be different but not our level of observance. Again, this is no doubt how he was raised.
If I were trying to bridge the gap, or at least keep the chasm from widening, I would not be focusing on the lack of observance of the people I am dealing with. Instead, I would focus on the inner strength they all show by stubbornly clinging to the beliefs and practices that were instilled in them by those they trusted most. Just as Orthodox jews stubbornly cling to theirs.