That idea that doing something terrible is okay if it's "just business", but not okay if it's "personal" seems to have entered pop culture in 1972 in the movie "The Godfather". It is pretty clear from the context that they were not referring to an idea that the audience was expected to understand.

After 1972, this "just business" idea is all over the place, often involving "business" that isn't business at all such as in the movie "Full Metal Jacket" where the line "nothing personal, it's just business" idea is expressed in almost those exact words. But it is two US Marines in the Vietnam War talking about the actions of the enemy in the war, not actual business.

This makes perfect sense when we understand that in the original context, in The Godfather, the "it's only business idea" wasn't talking about business either. It was members of a mafia organization discussing when they consider it okay to murder someone. The idea was that if it was done for strategic reasons to further the interests of their mafia family, then it was called "business". When it was done solely because someone had a personal grudge it was labeled "personal". In the movie, Al Pacino's character, Michael Corleone, wanted to kill the people who had killed his father -- mafia leader Vito Corleone. Michael was advised by others in the Corleone family that it was better to not to give in to such "personal" motives, but only to kill when it made strategic sense. Michael then made the case that it was "business" after all and gave a rationale based on that. The others were convinced and assisted Michael in murdering a police officer and a rival gangster. This is not real business. This is gangsters murdering people and calling it "business" as a euphemism for their organized crime operation.

I suspect that anyone who ever applied this idea to actual business probably doesn't understand the origin of the idea.