Did you read the article? Here is a couple of sections I think put it correctly:

When we see ourselves as fighting against specific human beings rather than social phenomena, it becomes more difficult to recognize the ways that we ourselves participate in those phenomena. We externalize the problem as something outside ourselves, personifying it as an enemy that can be sacrificed to symbolically cleanse ourselves. Yet what we do to the worst of us will eventually be done to the rest of us.

Often, all it takes to be able to cease to hate a person is to succeed in making it impossible for him to pose any kind of threat to you. When someone is already in your power, it is contemptible to kill him. This is the crucial moment for any revolution, the moment when the revolutionaries have the opportunity to take gratuitous revenge, to exterminate rather than simply to defeat. If they do not pass this test, their victory will be more ignominious than any failure.

It is possible to be committed to revolutionary struggle by all means necessary without holding life cheap. It is possible to eschew the sanctimonious moralism of pacifism without thereby developing a cynical lust for blood. We need to develop the ability to wield force without ever mistaking power over others for our true objective, which is to collectively create the conditions for the freedom of all.

Have mass killings ever helped us advance our cause? […] If we seek transformation rather than conquest, we ought to appraise our victories according to a different logic than the police and militaries we confront.

The image of the guillotine is propaganda for the kind of authoritarian organization that can avail itself of that particular tool. Every tool implies the forms of social organization that are necessary to employ it.

As a tool, the guillotine takes for granted that it is impossible to transform one’s relations with the enemy, only to abolish them. What’s more, the guillotine assumes that the victim is already completely within the power of the people who employ it. By contrast with the feats of collective courage we have seen people achieve against tremendous odds in popular uprisings, the guillotine is a weapon for cowards. By refusing to slaughter our enemies wholesale, we hold open the possibility that they might one day join us in our project of transforming the world. Self-defense is necessary, but wherever we can, we should take the risk of leaving our adversaries alive. Not doing so guarantees that we will be no better than the worst of them. From a military perspective, this is a handicap; but if we truly aspire to revolution, it is the only way. “The guillotine is the law made concrete… It is not neutral and does not permit you to remain neutral. Whoever sees it quakes, mysteriously shaken to the core. All social problems set up their question mark around that blade.”-Victor Hugo, Les Misérables

So we repudiate the logic of the guillotine. We don’t want to exterminate our enemies. We don’t think the way to create harmony is to subtract everyone who does not share our ideology from the world. Our vision is a world in which many worlds fit, as Subcomandante Marcos put it—a world in which the only thing that is impossible is to dominate and oppress.

And lastly:

Precisely because it is sometimes necessary to employ force in our conflicts with the defenders of the prevailing order, it is especially important that we never lose sight of our aspirations, our compassion, and our optimism. When we are compelled to use coercive force, the only possible justification is that it is a necessary step towards creating a better world for everyone—including our enemies, or at least their children. Otherwise, we risk becoming the next Jacobins, the next defilers of the revolution.

Or to put it in my words: Letting them live is the human thing to do, even if they pose a threat. Their power does not come from who they are but from the structures that are build around them. We have to dismantle those structures, killing people doesn’t help with that. If we have reached a point where we can guillotine them we will have already won.

If you want to execute them in self-defence (as maintaining capitalism is inflecting violence on the human race, therefor killing anyone doing it is self-defence). Go for it, but make it clear that’s why you are doing it, and that there is no better way. Like destroying all the methods they use and make them powerless which will also make them stop without losing your humanity (hyperbole).