Maybe. But not for long.

define justified," because I wanted to" IS a justification. honestly to be completely unjustified it must be accidental in which case many societies do.

Weregild.

Iain Banks envisioned a society that permits this, and much besides, in the (excellent) novel The Player of Games.

So what's wrong with the Vikings, why don't they fit your scenario? or the Romans or any number of other societies throughout history that considered raiding killing and looting noble pursuits . is it that you want them to also consider those within their own in-group legitimate targets? because that won't work for a lot of perfectly obvious reasons, not least being the minimal social cohesion and stability necessery to 'be' a civilisation, which you just can't have without some degree of trust that's impossible if the guy sitting next to you may just up and kill you whenever they feel like it

Looks like most of the answers are missing OP's point and going into the discussion of justification, while according to the question, it's 100% murders/manslaughters would become legal, and justification or morality become completely moot.

@Tom I love Iain Banks!! I haven't read that one yet but rest assured I'm definitely going to now.

Well, this has occurred historically. It also happens in modern societies. The US for example.

this reminds me of that Kino no Tabi episode about this kind of country kinosjourney.fandom.com/wiki/Land_Of_Permitted_Murder

I think any society of warriors, that praise strength and loath weakness, could potentially allow this. "If the victim is too weak to avoid getting killed, then the victim's to blame."

Saw that in a Science Fiction book, where the only requirement was that the killer had to pay for the funeral, and if they didn't, there was a severe punishment.

There's a (disputable) theory of modern nation-states, which is that one of their characteristics is to claim a monopoly on the legitimate use of force. Different states have different degrees of ability to actually enforce that monopoly, but it's difficult to reconcile any modern idea of "rule of law" with the notion that, in principle, society takes no opinion whatsoever as to whether arbitrary killings are permissible. So does your question ultimately mean, "do we need law?". Even libertarians want at least one law, which includes "no randomly killing people".

To what the society here refers to? As in the people and average population? Or the state and legal system? Or something else? This can change the answer.

@Tom I didn't get that from Player of Games...

"ok" as in no legal consequences whatsoever? surely some people would object, organize in militias, and create "murder-forbidden" areas, no?

The city of Commorragh in the WH40K setting is pretty close to such a society. You're allowed to stop someone from killing you, and allies of whoever you kill will want revenge, but aside from that the city is a happy-go-lucky murder haven.

By "kill", you mean "permanent ending of another human's consciousness"? No staying around as a ghost, uploading your consciousness into a virtual reality after death, getting absorbed into your murderer after death, or similar shenanigans?

We are already living in such a society. Oh wait, you are probably talking about the social acceptability of indiscriminate killing of humans, as opposed to other live creatures.

At the very least, you'd need a way for killings to not be significantly larger than births, or not larger than births for a significant amount of time. So, perhaps consider it being frowned upon?