Everyone needs a system of values and a way of understanding the world. Atheism having no built in values, forces you to self-determine your values. Now many people will ask "whats wrong with that?". Everything is wrong with that. You have no way of determining what values are right nor of perpetuating them even if they were right.
If you are just an individual with a frankenstein set of opinions cobbled together (all borrowed from worldviews that actually have built-in values btw, very few people genuinely have original ideas) then you have no "team" that can reliably perpetuate those values. You must remain alone, start your own movement, or sacrifice some values to join and perpetuate a pre-existing team. So with atheism you either have apathetic people, insular individuals with opinions, or random movements with no yard stick to measure which is right other than personal preference. On the other hand if you have religion you have a common operating system that can be perpetuated, shared coherently and serve as the core lens through which everything is viewed rather than individual subjectivity being your lens.
Sure you can be an atheist and have a philosophy or a political affiliation. Those are just cheap placeholders for religion when you are atheist. The properly ordered human psyche has philosophy/politics that EXTEND FROM religion. The more comprehensive a philosophical system, the more it starts to resemble a religion. In other words having a complete worldview becomes synonymous with having a religion either way, otherwise you are just ignoring the "big questions".
If you are truly agnostic you must sacrifice literally everything to remain consistent. You have no epistemic basis for ANY truth claim. If you are an atheist you must be a nihilist, so existentially you can say "everything is just materialism" but when it comes to values you are the same as the agnostic. If nothing objectively matters in your worldview and life is just having fun and/or suffering for a few decades with nothing after that, you can see why it generates selfish and shallow people. The lack of consistent/objective values is how you get people who are both feminists and in favor of islam taking over their country for example.
You may think it is dangerous not to "think for yourself" but atheism only leads to that in higher IQ atheists, and even then it isn't ideal. For the vast majority of atheists it leads to a combination of apathy and cognitive dissonance. They have no coherency to how they view the world and what values they do have come from outside of themselves anyway. They have no reason to reproduce because it gets in the way of their hedonism and they know they can't promise their kids that they will inherit a world worth living in. If they do have kids, the kids will be lost without beliefs and values and will only ultimately feel "whole" if they adopt a religion or a philosophy that mimics one.