Is the paradigm of Da' Mah LeHashiv limited to heretical Jews, and that of the restriction on teaching Torah to non-Jews limited only to non-Jews (excluding heretical Jews), such that there is never an instance in which one might need to use advanced Jewish texts to defend Judaism against a heretical non-Jew, or might be prohibited from citing similarly advanced passages that require background to understand correctly when engaged in defending Judaism agaist heretical Jews?
Example 1. A non-Jew approaches his Jewish colleague at work to engage in casual conversation lamenting the decline in society's "Judaeo-Christian values" with specific examples being contrary to Jewish law that is unenforceable without a Sanhedrin. May the Jew correct the non-Jew and explain the complexities of Jewish law and the limitations of enforcement?
Example 2. A secular Jew approaches an Orthodox colleague and laments the "Radical Christian" theology that believes in "hocus pocus", saying that, even though he's not religious, he can respect his Orthodox colleague's lifestyle because, "at least Orthodox Judaism doesn't believe in resurrection or a physical/literal afterlife." May the Orthodox colleague engage the secular Jew in a discussion of Perek Helek and the divergence of opinions between Rambam and Ramban, et al?