DY – non-religious people also have Neshamas and spiritual potential and do Mitzvos whether or not they know that’s what they are called. And a lot of them actually do know about and keep many Mitzvos.
You can’t really divide people up between religious and non-religious so easily. There can be “religious” people who aren’t really particularly religious (they just keep what they keep by rote, and aren’t really focused on Ruchnius growth), and there can be people who would be called non-religious, but really are very focused on Ruchnius growth according to their knowledge and ability.
A better question would be: Can an atheist truly have self-esteem? Or someone who is not an atheist but has no spiritual aspirations?