Then this is where you and i disgress.
A complicating factor or a hard choice? Sure
A mitigating circumstance? Maybe
An excuse? Absolutely not.
The question is not whether that culture drives a compulsion to commit violent crimes of retribution, its about whether we will stand for that as a civilized society. I for one am not going to let the poor treatment of indigenous people cloud the fact that sanctioned, violent retribution is wrong, and should be called out as barbarism, whether its migrant gang violence from the 70s, or this case here.
The theological or cultural beliefs of any group should not be above the law in my view.
Replace indigenous people with some other groups of Australians who have traditionally practised some pretty unsavoury practises, and see if you would be so apologetic or understanding of them.
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I suppose my use of "excuse" was misleading and more accurate ways to describe the background to what happened would be how you put it, either "complicating factor" or "mitigating circumstances".
I, like you, definitely don't think that just because he's indigenous and that's his culture think what he did is alright.
In essence, I agree with everything you mention in this post. My goal was to shed some light on the mitigating circumstances (see what I did there) surrounding Jurrah's fall from grace.