Being aware of cognitive biases doesn't render you immune to them. Others shape and inform our beliefs about the world just as our own experiences do.
You might be a "rational, fully self-realized, and atomized" individual but your behaviors and thoughts are certainly influenced by those around you. Here's a simple example: https://dictionary.apa.org/social-facilitation
Not everyone is brainwashed to accept group think no matter in what cirles they have to evolve in.
There are individuals and then there are the parrots who mindlessly repeat what the group says.