There is no such thing as an Atheists.

Regarding Scripture’s statements about slavery, again, simply put, we can divide the slavery regulations into those for Israelites and non-Israelites. Israelites could only be indentured servants, not lifetime servants (unless they so preferred their situation with their master that theyasked to be lifetime slaves). They were to be freed after 7 years and compensated generously for their time. They were also protected by several laws; they were not chattel. If a man took a female slave for a concubine, she had certain rights and could not simply be discarded.

Non-Israelites could be enslaved for life. However, they also had certain rights, including Sabbath rest in the household of their master. They could not be wantonly mistreated.

But we also have to ask: what would the alternative be? Israelites might be enslaved because of extreme poverty or because of being convicted of a crime. Slavery is not ideal, but it beats starving to death or being executed for a crime. Non-Israelites would be taken as slaves in armed conflict—again, most people would choose slavery to death.

In the New Testament, we must remember that Christians were a small minority. The Roman government had a way of squashing movements that openly called for slave revolts. But Christians had a way of gently subverting the order. Paul addressed slaves as people capable of choosing godly submission in the context of their slavery, but the really subversive part is that he called slave owners to treat their slaves as brothers and sisters in Christ. Really read the letter of Philemon and try to come to a conclusion other than that Paul wants Philemon to free Onesimus. In fact, church history indicates that Philemon did exactly that, and Onesimus became a leader in the early church.

Mopac might be but not spirituality of itself. What is "observable" is up for debate especially in the spiritual arena. Your assumption would only be true if you had not the medium or mechanism of that which transcends the physical boundaries to be observed. You of course have a physical layer, which perceives and experiences through the physical senses and material perceptions alone but you also have several layers beyond the physical and this is where the average atheist and theist part ways. It is through the layer or observation point beyond that of just the physical body which perceives the spiritual reality on many levels of conscious frequencies, it's much like tuning into a radio channel, your channel (medium) must correlate or harmonize (tune in) with the correct frequency before having any observation or experience.