So you have this apikores who writes that he doesn't believe in G-d or the next world, but he's raising his family to be very moral "lishma".
Let's just say that with these people when it comes to food and sex they say "screw the Torah", but when it comes to bashing the Hareidem for cheating and violence all of a sudden they preach morality endlessly.
Now let's see something. If there is no G-d and no next world that means that you come into this world just randomly, and when you die you just disappear. You may live long or you may die young in a car accident or whatever. Life is just random. And if life is just random then life has no meaning, and you just come and go like a puff of air. And if you just come and go like a puff of air then there is no such thing as good or evil. And if there is no such thing as good or evil then Hitler did nothing wrong. It's just survival of the most powerful.
If there is no accountability to a higher authority then there is no such thing as morality. Why should a guy not run around and rape and murder? What's the matter, it hurts you? So what! Life is meaningless anyway! You're not made in G-d's image, you're just a random puff of air! And so am I! Everything is just random. There is no authority to decide what's right and what's wrong. You say rape is bad, I say rape is good! I got the power so I win.
The reason why it's extremely difficult to understand this concept is because the moral operating system of the Torah is downloaded into every human being. It says that the Torah is the blueprint of the world. G-d did not make the Torah after he made the world. It's the exact opposite. He looked at the Torah and that's how he made the world. (zohar) The Torah is the operating system of the world. And this is why the Torah will talk about any subject under the sun, rated or not rated.
The nine months that a baby is in the womb an angel teaches him the entire Torah, and when the baby leaves the womb they make him forget everything. (Nedda 30b) Everybody tries to figure out what the purpose of this is. It could be that even though the Torah leaves the memory department the moral operating system of the Torah is still downloaded into the baby's subconscious.
Whatever it is it is extremely difficult to imagine a world without morality, and this is why the apikorsim preach morality all day long. So it turns out that the apikores himself is the greatest proof of G-d's existence since he cannot stop preaching morality "lishma". And if everything in this world was just "random" there would be no morality.
You might want to bring proof from the Nazis that there is no G-d because they had no morality. But this is not true, they had plenty morality. The first thing they did was to outlaw kosher slaughtering because they held that it caused pain to the animals. And even though the Torah says that slaughtering the right way will not hurt the animals, they nevertheless held that it did. And not hurting an animal is a Torah value. In fact, a person may not even eat until he feeds his animals. (Brachos 40a)
"Whoever slaughters people can kiss the calves" (Hoshea 13,2 Sanhedrin 63b) This was talking about Jews who sacrificed their own kids to the gods. (calves) Moishe Abba Kamyan used to apply this verse to the Nazis.
Another thing is that the holocaust did not happen in 69 when the hippies were running around half naked. It happened in 39 when the men wore hats and the women wore skirts, so don't tell me there was no morality. JFK was the first president to take off his hat, and his wife was the first to have a skirt above the knee. "If JFK would only have been wearing a hat"........
According to this reasoning if the Torah would have said that all people should hit each other once a day, then hitting would be good and not hitting would be evil. And then the apikores would say "I don't believe in G-d but I still hit morally "lishma".
P.S. Just because the world runs on morality this does not take away the free choice to do good or evil, or to turn morality upside down. like PETA who asked Arafat not to use donkeys for suicide bombings, and the bleeding Jews who have compassion for the wicked. "Whoever has compassion for the cruel will end up being cruel to the compassionate" like what happened to king Shaul and Amaleik. (Shmuel 1,15 Yoma 22b)