Agnosticism is about knowledge.

What is Atheism?

"Atheism entails, minimally, the disbelief[1] in the existence of any deities.[2] It is contrasted with theism, the belief in a God or gods. Atheism is commonly defined as the positive belief that deities do not exist, or as the deliberate rejection of theism.[3][4][5]

However, others define atheism as the simple absence of belief in deities[6][7][8] (cf. nontheism), thereby designating all agnostics, and people who have never heard of gods, such as newborn children, as atheists as well.[9][10]

In recent years, some atheists have adopted the terms strong and weak atheism to clarify whether they consider their stance one of positive belief (strong atheism) or the mere absence of belief (weak atheism).[11][12][13]"

I know I've answered this before. But recently a friend of mine asked why (so called strong atheists) believe "a negative- something that can't be proved."

Here is a quote from Richard Dawkins:

"A friend, an intelligent lapsed Jew who observes the Sabbath for reasons of cultural solidarity, describes himself as a Tooth Fairy Agnostic. He will not call himself an atheist because it is in principle impossible to prove a negative. But "agnostic" on its own might suggest that he though God's existence or non-existence equally likely. In fact, though strictly agnostic about god, he considers God's existence no more probable than the Tooth Fairy's.

Bertrand Russell used a hypothetical teapot in orbit about Mars for the same didactic purpose. You have to be agnostic about the teapot, but that doesn't mean you treat the likelihood of its existence as being on all fours with its non-existence.

The list of things about which we strictly have to be agnostic doesn't stop at tooth fairies and celestial teapots. It is infinite. If you want to believe in a particular one of them -- teapots, unicorns, or tooth fairies, Thor or Yahweh -- the onus is on you to say why you believe in it. The onus is not on the rest of us to say why we do not. We who are atheists are also a-fairyists, a-teapotists, and a-unicornists, but we don't' have to bother saying so."

Why should we leave the philosophically comfortable and safe position on agnosticism about God and postulate [below] a positive proposition like Strong Atheism?

"Strong Atheism is the proposition that we should not suspend judgment about the non-existence of a god or gods. More extensively, it is a positive position against theistic values, semantics and anti-materialism, a rational inquiry in the nature of religious thought, a new way of thinking about religious and spiritual issues."

There are good reason to not believe.

Empiricism, Science, problem of evil, the god answer solves no problem, the gambit jumbo jet.

Hence if knowledge says there is only a small infinitesimal probablity that the supernatural exists, we shan't believe.