The very science atheists love and glorify of tells that without a controlling force things will end up in chaos. Just the rules are not enough there has to be a force to enforce those rules.
Atheism by itself may at times have a technical explanation of observed phenomenon, but it doesn’t have anything to enforce good conduct.
All old age religions provide a framework for good conduct. It keeps dubious individuals of the society in check, and supports well behaved individuals. Being religion it also provides a self-motivating mechanism thus not requiring any enforcement. (Please read the book called punished by rewards that explains why self-motivated behavior is far far superior compared to an enforced behavior).
And one may argue that the constitution and the law of the land should enforce good behavior. But that is the enforced implementation. In absence of the force the behavior will drift – can’t be guaranteed. Thus, a better way to ensure good behavior is self motivation. So that’s where religion comes into picture.
Thus we have established a need for organized religions. In any society you will find a large number of followers, a few good leaders, and a good number of crooks and fundamentalists trying to be leaders.
If good people decide to stay away from organized religion then what is left?
You have a large number of followers, however, because good people are staying away from leading them, so the crooks or fundamentalist lead a group of blind gullible followers. The net outcome in that scenario would be fools strapping them with the bombs and blowing up good innocent people or do dubious things under the pretext of the religion.
Thus it is important for well meaning folks to stay a part of organized religion. It is a symbiosis.
So now we have established that there is reason/need for an organized religion and for good people to be part of that religion, the question is what religion do we follow. That’s where you will understand the importance of Sanatana Dharma. It’s the only religion that is at peace with modern science, with atheism, with other religions, with itself, with one god, many gods, god with human form (including female forms), god with no form, god in animal like form, and allows itself to adjust as per the time place and circumstances guaranteeing acceptance of all the hitherto unknown philosophies as well.