I still haven’t come up with something that I feel fits the spirit of the question, but my start is that I could tell Archimedes about atheism. Up until I was maybe 11 or 12 years old I never really considered the question of religion. My parents taught me the basic Christian tradition, but I never attended church or was deeply indoctrinated. At that age, though, other kids started asking me about religion as they began to become adult members of their religions. “What religion are you?” they would ask and my answer was “I don’t know”. Someone asked if I celebrated Christmas and I said yes so they told me I was a Christian, but I didn’t really know what that meant. But over the next several years the more I learned about religion the less it seemed to make sense to me, until eventually someone shunned me for being an atheist, so then that put me on the path to actively learning what atheism was and seriously thinking about the question of whether anything supernatural exists.
In the end I concluded on atheism. If I recounted my steps to Archimedes, I think they would come through clearly, except rather than the Cult of Jesus he might hear Cult of Zeus. To what extent this might actually improve things I don’t know, since I’m not even sure if promoting atheism for its own sake is a good idea.
In sum, I agree, but one small issue I take is when you argue that someone acts contrary to their learning it demonstrates that they don’t really understand it. I’m sure this is often the case, but sometimes it’s a matter of akrasia: the person knows what they should do and why, even deep down inside, yet finds themselves unable to do it.
Humans suffer heavily from their biases. I recall at in middle school I came to the conclusion that no deities existed, yet it took me a long while to act on it because of social pressures, so I continued to behave contrary to my beliefs out of fear. It was only later in life that I gained the self-confidence and bravery to act upon my beliefs, no matter how contrary to the social norm.
You might say that I didn’t really understand and that if I did I would have acted differently, but I find this contrary to my own experience, and this is only one such example. The human brain is a mine field, and even when we understand, we may still fail to act correctly.