It is a very simple issue that gets overly complicated by semantics and preconceived notions.
If you are asking if atheism should be a religion, then that is a none question. It has already been pointed out in debates with theocrats that not believing in something is not an ideology or a philosophy. It is merely the absence of being convinced of a given claim.
If you however ask if there should be a religion of science/skepticism/humanism. A “religion” that combines all of those underlying concepts that generally lead to atheism then that is a different question and one I happen to think the answer to should be yes. Once again things get complicated here because atheists who themselves don’t feel the need for such a philosophy will say it is a bad idea just based on the fact that they don’t want to be in it. But that is kind of missing the point, it would be more accurate to ask if it would do good and if it would cause harm and I can’t see how it could have anything but positive effects. The other complication comes from the fact that the word religion kind of carries a lot of baggage. It does so because today we draw a distinction between factual based science and faith based religion but the word religion traditionally has made no such distinction. The term has pretty much stood for a framework for understanding the world and how to best interact with others in it, it only happened that back in the day all of the ways of understanding the world were based on faith.
So if we for a moment could just ignore the word religion or accept that it does not mean anything metaphysical but it can be a life philosophy that takes nothing on faith, and if we can accept that maybe all of us are not interested in being a part of it ourselves, but it will do only good for mankind so therefore it is worthy of support then you could go ahead and ask what such a religion would be.
I find it hard to not imagine how one could design a scientific “religion” that would without a doubt further human society incredibly. Imagine that is completely scientific and takes on the shape of something like Buddhism while combining the methods of critical thinking and skepticism and the ideas from science on how to make sense of the world, with all the things we have learned from neuroscience and positive psychology about happiness and well being.
Basically a religion in which you go on a life long journey of self improvement, both intellectually and emotionally. You strive to learn to understand and control your emotions to reduce how anger and fear and jealousy etc influences our ability to come to rational decisions, you strive to learn how we are mislead and how we jump to premature conclusions (aka the ways of incorrect thinking that leads people to join conspiracy theories or misjudge the value of evidence for new age medicines etc), you learn from positive psychology about how happiness actually works and which things in life we wrongly think make us happy and what things actually do have a huge impact on our well being. A constantly ongoing journey of understanding your own mind and how it works and become objective and more reasonable, combined with a strife to help others and be happier and all of it with the highest goal of constantly gaining more knowledge about the natural world and how things work.
You could even have a “bible” of easily quotable soundbites from well known thinkers that sum up the principles of the life philosophy. But instead of having
leviticus 25:45 - You may also buy some of the temporary residents living among you and members of their clans born in your country, and they will become your property.
it would have
Sagan 12:18 - For me, it is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring.
Would it be something for everyone? Probably not. Would it be better than every single religion that ever existed? Without a doubt, would people who follow this religion be better off even compared to the people who believe in no religion and are not skeptics or rationalists like us but the every day Joe who does not stop to think about these issues at all? Probably.
A religion like that would insulate everyone who follows it from being taken in by sects, cults, new ages bullshit and pseudoscience because it equips people with the tools to not get taken in by false information. It would be more successful most likely than our current methods of trying to increase the number of rationalists in the world because it has many more weapons with which to expand. A tax exempted rationalist temple in every city with pretty colors and a symbol above the front door where people see others go in would without a doubt draw in people that we currently don’t reach.
As I said, it might not be for everyone, and people could surely make philosophical arguments for why this is not ideal, but I can’t see how it could not be of pretty much only good, and if we want to survive another 100 years on this planet it seems like we need the majority of people on earth to subscribe to a much more enlightened philosophy than they currently are.