Agnosticism simply means to be without gnosis (knowledge). No one can “know” for absolute certainty of many things in the cosmos. Life, as the old Madonna song goes, is a mystery. Science is the revelation of truth, but by its very nature, even science changes with new knowledge. Also, there is so much more to what is possible, then just what people know to be possible.
To claim certainty, or to own the “truth” is to possess god, and being possessive about any truth is what leads to exclusion, war, and hatred. If humanity were just to embrace the ideas taught by religion, that people should be good toward living things, all would be well. But the fact is, people want certainty so badly, they will defend till the death their right to claim it. Overall, religious fanatics are more known for torture and barbarism than atheists, but no claim for owning the truth, ever works out well for anyone, if it is an exclusive claim.
The fact is, people, care much more about being right, then about being good.
All beings long for belonging and connection, and atheism, as well as religion, promulgate the idea that only a chosen select few, are in the know. The rest of you losers are gullible idiots, in other words.
Religion often teaches that the gullible are tempted by Satan, whereas atheists often feel the faithful are tempted by wishful thinking.
Once upon a time, it was an absolute truth that human beings (physically) could not visit the moon. Then history changed, and it became something possible. New information, new technology, and new facts occur every day. Those who purport to have certainty, to know, can never be one hundred percent “knowing” in light of this. For all we know, we could be living in Neo’s world of the matrix, as even senses can occur in dream states.
This does not mean there are no good arguments against the existence of god(s) or an afterlife. The existence of a flying spaghetti monster, or that there is an evil monkey in your closet can not be factually assessed by anyone. It certainly looks that way from the condition of most people’s closets as they find them in the morning rush to dress. However, one cannot prove any faith-based belief. What science can prove is that which can be tested empirically and retested.
It is right that all people should use critical thinking skills.
It is also true that people, as Einstein said, need to constantly expand their circle of belonging and compassion to include all life and creation.
If this idea is false, as it is not provable, then perhaps the same invisible evil monkey in your closet is also disordering all of our thinking ability. Who can prove it is not so?