In the original manga & anime, Atlas was created by a dark-skinned man to use as a tool of revenge against whites who had by their racist policies, caused the death of the man's wife. However, the man was as abusive of Atlas as whites had been of blacks. For, he created him with sufficient intelligence to carry out his mission, but this also gave Atlas the ability to know that he was a slave & to resent it. He therefore, turned against his master.
The 1980s Atlas was a combination of the new (cute) Atlas as seen in manga vol. 23 & the Blue Knight. Although it seems clear that the BK's story became the focus once Atlas "grew up."
Atlas' original story was discarded as he became the (then) new Blue Knight. Thus, Atlas has a dislike of humans because Guiss, Skunk, & the other bad guy had abused him. While at the same time, Livian showed him kindness, which caused him to be more accepting of other robots, rather than totally alienated. Also, because L admonished him to be kind to those weaker than himself, he seemed to be hesitant to harm humans who had not first harmed him.