Oomis: I never understood that argument. We don’t determine a Jew according to what the goyim think.
And in fact, goyim who had a Jewish father or other Jewish ancestor were also considered Jewish by the Nazis and persecuted and killed just like the Jews were.
And it certainly doesn’t apply here. Is it ok for a ffb to want to be not religious and we say, oh, no problem, at least you remain a Jew since the goyim will still consider you a Jew.
Now your message itself, that we shouldn’t look down at others who are (in our minds) “less observant” is well taken.