The only good thing about Assassination is when it is used to END a war much sooner than otherwise in order to save lives, on both sides. If it can not achieve that end, saving more lives than it takes, then it's wrong. It is always wrong to kill, IMHO, but sometimes killing is necessary in the defense of innocent lives. For instance, if you are being mauled by a rabid dog, would you rather someone stand around watching you get torn up, doing nothing at all, or would you rather they kill the dog? The poor dog is ravaged by a brain eating disease, it's not really at fault, but still, it's either you or the dog. Which do you choose?
As for me, I'd rather they figure out a cure to the disease, tranquilize the dog, and cure it. I consider dogs to be people too, just more like 2 or 3 year old kids than adults. Do you abuse kids for the fun of it? No? Then is it OK to abuse dogs? I say, uh,.... well... NO!! If you like abusing animals, hurting them, demeaning them, being cruel to them, it's not much of a step up, or whatever, to start seeing humans as just meat puppets to play with too. The connection between animal abusers and murderers and rapists is well established! People who bathe their brains in the sick pleasures of cruelty will have little compulsion against moving on to being cruel to Humans.
So, people who kill animals without any kind of remorse, without any kind of feelings at all, are less likely to have a compulsion against killing humans. But people who raise animals for food, and actually care about how the animals feel and live their lives, may actually feel bad about causing them pain and will be more likely to kill them Humanely. The only humane killing of a human, BTW, is one which they choose, like when they are suffering horribly from a terminal disease, with no hope of improvement. Those people deserve the right to die, by their choice.
But let's go back to assassination. Perhaps we need an official Assassins Guild in our society, individuals trained to kill people in the most humane possible way, and only do so at the greatest need, like defending the lives of innocents, or when someone chooses to die they can employ an Assassin.
I read a book about Immortals, and in their society where there were still mortal people as the majority, a person had to prove that they were a great asset to society in general in order to complete the process of becoming immortal. If they failed to do so within a certain amount of time, like 5 years or something, then the process which had begun to change that person into an immortal was halted, and the person was taken away by the Assassins, to die a humane death. Why? Because of population control, I guess. You can't have Everybody ever born become immortal, right? But the problem was eventually solved in a different and much better way much later in the book. I won't spoil it, just find it and read it. I can't remember what it's called, unfortunately, and I don't know how to find it. One of the characters was an immortal named The Jacinth Martin, I think. And they achieved immortality by genetic manipulation, drugs, and cloning, with the ability to synchronize the brains of the clones with the one that is awake and doing things.
If I were going to assassinate, say, the President of the United States, I wouldn't broadcast my intentions, or tell anyone my plans, or even keep anything at all on paper or digital form. I'd keep it all in my head, and provide no clue whatsoever to anyone that I'm about to attempt to kill the President. I am totally incapable of doing any such thing, but, if I were, and I were inclined to do it, that's just one of the many things I'd do. Since I'm no assassin, and I'm disabled, there is very little chance of me doing anything like that. In fact, my personality is such that I'd probably just throw a pie at his face. Hahahaha! Yah! Pie in the face!