Last time i checked you can't go around killing anybody you want for whatever reason,since it's kind of against the law.
The law isn't going to stop me from killing someone.
The law is only going to come along after the fact and decide whether or not it was justified.
A parent can kill their kid for whatever reason they use at the time. Our outrage, debates, and hearings later are all quite irrelevant to what a person did/didn't do or could/couldn't do. Obviously - they did, and could.
I could poison all of the people around me who I hear use the word "folks." Whether or not I should is quite irrelevant once I've chosen to do so. At that point, it is only a matter of whether or not some outside force intervenes.
If I were to gather enough people together who desired to do the same things - I could easily supplant the local authorities and make it difficult for regional (county/state) authorities to enforce the law. I could decide that I don't want any red shirts on my planet, and get enough red-shirt hating people to go around and search homes to pile up and burn red shirts (if the people refuse to take them off, some amount of collateral damage is acceptable for the end goal).
Obviously, this is 'illegal' - but if the police get added to the pile of burning things and the SWAT teams are driven off ... it doesn't really matter whether or not it's illegal. It's happening until some entity with the will and means to stop it intervenes.
Russia broke "international law" (whatever that is) when it took over Crimea.
.... Shame on Putin.
...?
"You don't invade countries for natural gas while holding rigged elections. This is the modern world and we're beyond that."
Well - obviously not. Russia just did, and it looks like they are getting their way. Now, I'm not saying we should counter-invade or anything like that. I'm just saying that we can sit here and talk about how countries in the modern world behave, how we don't invade each other, etc... it's all quite meaningless if a country is able to seize territory after territory while getting what it planned on getting.
Similarly - we don't go around killing each other for whatever reason... until someone is shooting up a school for whatever reason. Then it really doesn't matter what the laws are - that event will continue to unfold until someone puts a stop to it.
We don't go around stealing from each other... until someone does. Then they realize they can get what they want for free, and continue... until someone puts a stop to it.