An enemy of civilization, a "de civilis hostis" is a legal concept present in many species' and governments' histories and legislatures. It defines a person being so reprehensible that their acts have alienated themselves from society at large and set them outside the protection of law. As such, engaging them in violence carries no legal repercussions.
Historically the most wide-spread definition for an enemy of civilization has been a pirate. Torturers and slavers have been also considered to be these in certain jurisdictions, but cultural differences between species have prevented them from being included in wider definitions.
Due to wide breadth of colonized space and limited reach of organized governments, piracy is commonplace and even encouraged due to economic and political interests in anarchic reaches of space. As a result, this concept is only popular with said civilizations, such as those of Citadel Space and few established Terminus and Traverse states.
On Earth, the concept has been known prior under the name of "hostis humani generis", enemy of mankind.