Religion, just in and of itself, isn’t really the problem. It’s just the most notable example of the underlying problem, which is probably best summed up as aggressive tribalism.
People have a compulsive desire for self-affirmation - for assurance that they embody whatever qualities they consider the indicators of “good” people. And by far the easiest way for people to assure themselves of that is to associate those qualities with a label and self-apply that label. That gives them a fellowship of label-wearers who are invested in the same belief, which establishes a feedback loop in which they all assure each other of how [good/right/strong/smart/etc.] they are, and a ready-made set of outsiders they can individually and collectively condemn. And that last is the real problem - since few if any people truly embody the qualities they wish to believe they do, the easiest and most effective way to assure themselves they do is to focus on some designated set of others and on the assertion that they fail to possess those qualities. That allows people to assure themselves that they are at least more [good/right/strong/smart/etc.] than these other people over there.
That’s clearly a toxic and antagonistic dynamic that really just serves to divide people up into warring factions, and since it’s at least somewhat irrational yet crucial to people’s self-affirming self-images, it’s a thing that easily gets entrenched and, whenever possible, codified, so that it can be forcibly imposed.
Again, religion is certainly the most common and historically destructive vehicle for that, but it’s far from the only one. Most notably, it’s also the dynamic underlying virtually all ideology and a great deal of philosophy, not to mention a great many less significant distinctions, ranging from sexual preference to diet to sports fandom.
Now - in the first place, I would say that it would not have been possible to have a world without religion, since the practical purpose of religion is to provide answers to questions for which there’s insufficient evidence or knowledge to support nominally legitimate answers, and that lack of evidence and knowledge was an unavoidable part of our history. From the moment that somebody wondered what that big bright thing up in the sky was and somebody else made up an answer for them, religion was inevitable.
Beyond that though - if we were to imagine a world in which religion somehow never came to be, we’d just have had a world in which people would’ve focused that much more on the other ways in which they divide themselves against themselves, since that desire for self-affirmation exists anyway.
And truth be told, I actually think that’s part of the problem with our current world - that a great many people have just shifted from what would in the past been a self-affirming faith in a religion to a self-affirming faith in an ideology or philosophy or political affiliation or some other tribal distinction - that much of what we’re seeing today is the same toxicity just based on more secular divisions.
Not that religion has become less of a problem - what it’s lost in overall market share, it’s undeniably gained in the fervor and aggression of its remaining adherents, but it’s also been joined by a wide range of other divisions, each destructive in the same general ways, even if not necessarily to the same degree.