i am surprised that even atheists consider themselves sinless.
two possibilities occur to me
1,sin is too religious a word.maybe going against the conscience?if they think they never do that,it speaks to me of shutting off the sense of wrongdoing and not being able to recognize it anymore.
2,not having any point of reference as a final authority they determine right and wrong on whatever suits them.this admittedly seems consistent with atheism.
maybe the sinless ones could enlighten those of us that are conscious of being sinful what they mean?