There is a notion that a police officer, a public servant, or even a politician can justify (or avoid having to justify) their actions by the simple phrase 'just doing my job'.
The police officer who arrests someone for a victimless crime may be violating someone's rights (to do what they like with their own body and possessions unless they are interfering with someone else's). But he doesn't feel any need to justify his actions beyond 'just doing my job'.
Apparently someone is paying him to do that job, so it must be morally right. Is a contract killer entitled to the same justification? Or a mafia stand-over man perhaps? Both are 'just doing their jobs' when they violate people's rights.
In the case of the police officer or the public servant, their paymaster is the government. Does that mean that the government is infallible? That no government could ever pay someone to violate someone's rights or to do something unjust? Does it matter if the government is democratic? Is a democratic government incapable of error because it is elected by the mob? Is a mob incapable of error? Or only incapable of error if it is big enough? How big does a mob have to be before it becomes infallible?
The person who uses the justification is 'just doing my job' has abdicated their morality for government policy. For this person, right and wrong cease to become moral terms and are just statements of judicial (ie political) position. And truth becomes merely the outcome of an argument in court between lawyers.
Anyone who uses this excuse is a moral vacuum and an oppressor.