Is "being able to pass for the majority whenever one wishes" the same thing as "being in the majority?"

Can we? Perhaps. I think most Jews who identify themselves as such either can't, or choose not to. I don't think Jews are inherently high yellow. But our ability or willingness to assimilate is complicated by the varied relationship between Jewish observance and Jewish cultural identity, as well as the level of our desire for acceptance.

fjm's comment that erasure isn't assimilation seems very apt.