While that is an objective decision, it is made by relying on subjective values:
>Pro: They die
How do I decide that they must die? Most likely because they did something to offend me, however what it was, and how I decide that it was enough for murder, is down to my moral values.
>Jail = Impossible approach to revolution
Why is revolution objectively good? A porky wouldn't want to do it. A libertarian true believer would find the authoritarianism needed for it abhorrent and so on. It is, again, a moral question.
>Don't stab them unless it's a justifiable motive
Exactly. So how do you justify it? You can only be objective about it after knowing what it is you want to achieve, which is a purely value-based question.
Let me try to quickly attack some counter arguments I've heard before:
<But morality is an ideological construct by the superstructure, and is mostly determined by material conditions
So? It still exists, and you still can't make any decisions without it.
<Something something maximize entropy
It is still a moral statement. You want to maximize it as you believe it is a must for there to be existence, however believing that there should be an existence is a subjective view. People like gnostics and anti-natalists only prove that you can take an opposite stance, no more rational or irrational than yours.
I doubt such really exist, and also they would still be values against which, theoretically, you could take an opposed stance.