church of Christ (coc) and legalism

Why do i find that many who left the church of Christ (coc), have left christianity altogether and have become atheists? Whatever it is coc'rs preach and do, they somehow seem to be using Gods word to drive people away, rather than bring them to Him. Satan must be mighty pleased. They do his job using Gods word.
coc's says everyone else but them are deceived, but i wonder if they ever considered themselves to be the ones deceived in the first place.
They seem to quote verses out of context to support their doctrines, but never seem to get the complete picture of the gospel, even the whole bible that it is by grace through faith one is saved, that it is not what we do but what Christ has done that saves us. Read Eph 2:8-10. Dont forget vs 10. And try to figure out what it means.