do you think that atheism is a belief just like theism is?
No, but I also don't consider theism a belief system. It is a class of belief systems that need have nothing more in common than a god belief, just as atheists need have nothing more in common than no god belief. Whatever else a theist or atheist believes comes from elsewhere. For the theist, that's a book and a pulpit. For the atheist, that's usually the same principle that brought him to atheism just described applied to the subject of gods. Apply the same principles to political philosophy and we come up with the modern, liberal, secular, egalitarian, democratic state with guaranteed personal rights. Apply the same principles to epistemology and one replaces effete faith-based systems like astrology and creationism with science. And put it all together into a single worldview and one arrives at humanism, a philosophy based in reason, empiricism, and empathy.
Atheism isn't a system of beliefs, but it is the sound conclusion of reason applied to two beliefs, namely, the belief that ideas need to be sufficiently justified according to the tenets of critical analysis before being believed, and the belief that no such evidence exists for gods. Atheism generates no new beliefs of its own. As indicated, those come from elsewhere.
Nobody can say they know that life did not need at least one of those imaginary gods to get started.
Agreed. Also, nobody should believe that life required a god
what science knows from observation is that life comes from previously existing life.
Nobody can say that they know that life didn't originate from nonlife. You might not realize it yet, but creationists also believe that it did. They believe that God is the source of life in the universe. That's life coming from nonlife right there unless they consider a disembodied consciousness life, in which case that spirit is life that didn't come from other life.
I have heard some atheists claim that they have a belief that there are no gods.
They don't define atheism. They are a subset of atheism. Most atheists are agnostic on gods, since they understand the limits of knowledge in this area. It is presently impossible to rule the existence of gods in or out, which is grounds for belief among theists, but grounds for unbelief among skeptics, who need more before believing.
If God were so easy to find, believe in, and understand, He would not have allowed the serpent to turn Eve's mind around. God wasn't standing there when the serpent tempted Eve, telling her at that moment, "No! Don't do that!" Even if He had been, she might not have believed God. Yet He exacted the penalty.
Humanism rejects this and considers it unethical. If I were to invent a god, it would have my values, too, but not those. These are the values of the abusive, malevolent parent setting its child up for failure and then punishing it for so doing.
You might find this of interest. It was written by a man named Richard Banford:
"Do you know [my god's] name? Sure you do. He talks to you every day. You could not live a normal life without him. You believe in him, whether you like it or not. Unless you abandon him completely, you cannot deny he exists.
"My god is a more personal god than yours can ever be, for if you have enough sense to understand these words, my god lives within you. He lives within us all, to some degree. A heartbreaking few cannot understand him, but this is not their fault. The real tragedy is the multitudes who ignore much of his counsel, particularly when he questions your god too deeply.
"My god has been around longer than your god. He was here before the many other gods that preceded your god. Though you will likely scoff at the notion, my god was the father of your god, as he was to all gods. But that was long ago when he was young and not yet sure of himself. Though many of your god's followers try to hold him down, my god grows stronger and more independent each day.
"When your god expelled us from paradise for eating an apple, my god taught us to grow our own fruit.
"When your god forbade knowledge, demanding we live in ignorance, my god created books.
"When your god smote cities like a tantrum-prone child, my god helped to rebuild them.
"When your god insisted the world was flat, my god showed his followers it was round, to their peril at the hands of your god's followers.
"While your god watched in silence as children sickened and died, my god created medicines to make them well.
"When your god winked and nodded at slavery, my god argued passionately against it.
"While your god represses half the human race, my god considers woman to be the equal of man.
"When your god only helps those who help themselves, my god rolls up his sleeves and actually does help until your god decides to join in, and then steals all the credit.
"When your god inspired great buildings and great art, my god made them possible.
"While your god says we are all born sinners, tainted before we even draw breath, my god says we are all born innocent; a clean slate with limitless potential.
"While your god offers dubious allusions of an afterlife, my god provides for us here in this life.
"While your god makes amazing promises, but offers not a shred of proof, my god performs amazing deeds, and the proof is there to be seen by all.
"While your god demands blind faith and obsequious obedience, my god encourages questions, even about himself.
"When your god says "Thou shalt not," my god says "You can do anything."
"My god is reason. He does more in a day than your god will ever do."