So much to say to compliment and complement this one. I'll start with my personal definition of spirituality that does not require a belief in a higher power. When I use the term spiritual, I use it in a manner that transcends the binary of theism/deism versus atheism. One can act entirely spiritually with or without a belief in “god” however one understands that term. Spirituality only requires love, empathy, compassion, humility, honesty and courage. As I define spirituality, there is a flip side to the coin and all those positive feelings— accountability, both personally and holding others accountable for their words and deeds. Not necessarily punish or judge, but not turn the other cheek either.

Putting lesson plans aside, I believe the number one reason for atheism, which in and of itself is as dogmatic as the most orthodox religion, is that many religions have corrupted the message of what God is. Religions have been designed to be believed and thus construct God as a deliverer of human wants if we do as we are told, which God is not. So people either blindly believe in God because the lie of what God is is believable, or reject God because the God defined by religions cannot co-exist with the reality that most people do not get what they want, or are not actually happy, and a world full of seemingly senseless tragedy and really bad things happening to good people.

So the reason that atheists insist there is no God is because they correctly insist that the nature and role of God as taught by religions is mistaken.

If anyone wants to read essays that I have written that discuss these views that I have summarized here, there is https://medium.com/illumination/why-is-it-so-easy-for-people-to-believe-the-most-obvious-lies-yet-require-proof-of-god-339a2a07cc4f and https://medium.com/know-thyself-heal-thyself/how-do-you-define-god-9898492eae9.

I'll be leaving a couple of other comments tied specifically to lines in your post.