In many historical legal systems, in particular European systems, there existed a concept known as 'Outlawry', literally a state of being outside the law.
It was generally considered to be a punishment, and an extremely harsh one at that.
If an individual was declared an Outlaw, then they could not use the legal system to defend themselves and other individuals could punish them with as they saw fit with no penalty of law. In some times and places it was a crime to help a outlaw in any way, to so much as give them food was considered aiding and abetting.

In particular, the concept of Outlawry in historical polycentric legal systems is worth noting, as it provides an interesting model for comparison. A polycentric legal system simply lacks the apparatus to uniformly compel people to participate in it, it must convince them of the benefits of participating.
If an individual chose to disregard the legal system then it would in turn, turn a blind eye to that individual. An individual would be free to ignore the legal system but could not then count on it if they needed it at some time in the future.

So why do I think this is relevant? The legal system (to the extent that we have one) in Civcraft, is functionally a polycentric legal system: no central authority (in game) can compel anyone to do anything as they can just log off and at worst can be confined to The End (if captured).
As such any legal system within Civcraft must convince people to participate in it. Nevertheless, some individuals have decided in advance to not be convinced thereof, no matter what. Their sole objective to kill, to steal and to destroy.
I refer to such individuals as Griefers, although many of them seem to call themselves Raiders. Perhaps it makes more sense to call such individuals Outlaws, it is what they are after all, individuals who have decided to be outside the law.
Outlaws disregard the law when it is convenient for them to do so and thus cannot (and should not honestly expect to be able to) rely on the protection of law when that would be convenient for them.

Particularly dangerous Outlaws are likely to met with violent resistance upon being sighted by a would-be victim, this is a simple precaution against a very probable and credible threat of grievous harm to the would-be victim. Whether this response is subsequently found to be proportional or reasonable is one matter however it is the most likely outcome of such an interaction.