Much of today's political discourse, regardless of faction, is focused on presenting one's own faction as being pure and impeccable, while presenting any other as either innocently cooperating with evil, or directly malicious. That is to say, all atrocities committed by the faction we favor must be either justified or denied, while all atrocities committed by opposing factions must be emphasized, exaggerated, or even fabricated.
If this behaviour is viewed with (a lot of) charity, it could be viewed that the denial of the evils our factions commit is because we recognize that it is evil, and the emphasis on the evils of the other factions is precisely to show the dangers of those ideas. But the problem with this kind of strategy is that absolutely every faction, even the ones we believe to be the most benign, is riddled with a history of atrocities and evils. Even our modern-day Liberal Democracies, which we put on a pedestal as the most humane of systems of governance was only able to come about through violent revolution, mass executions, and persecution of the Church. Even today we see its violence in the form of the killing of children in the womb and of the elderly or sickly (i.e. abortion and euthanasia).
The truth of the matter is that atrocities and violence are not particular to any given faction or ideology, nor are they absent in any faction or ideology. The only ideologies without a history of violence are those which have never had the opportunity to act. This is because violence is the result of the fallen human condition. It is but a naïve dream for anyone to believe that their particular solution for the administration of the public sphere (i.e. politics) will be free of any kind of violence. Truly, it is the silly dream of those Utopian Socialists who aimed to create a Kingdom of God on Earth. For only through Christ's Parousia will we reach such a state. Any other attempt to do so, being only by the strength of Men alone, will ultimately culminate in disaster.
All this does not deny, certainly, that certain ideologies lead to more violence than others - or simply ideologies in general. It is undeniable that certain ideologies have founded themselves upon the justification of violence by denying that it is violence to begin with. But to simply say that there are worse ideologies out there is no excuse for the violence committed by another.
All this is very much akin to Puritanism. We portray ourselves as pure and impeccable. An inherently Pelagian idea. Therefore, to say that a given faction is worse than our own because it has more atrocities, while all of ours are justified, is negligent and a justification for violence in and of itself. The argument means as much as a drop of water in the desert.
So how should we approach atrocities? Because obviously they are evils, and we should denounce them and try to avoid them. Firstly, we must refrain from comparisons. To compare our evil with the evil of another does nothing more than to confirm the human condition. It is another thing if another is purposefully justifying evil, which is condemnable. But we must refrain from a holier than thou attitude in this regard. But secondly, and perhaps most importantly, the solution to Puritanism in the political sphere is exactly the same as in the personal sphere (as with so many other things): the great virtue of Humility.
Yes, we must denounce our own atrocities and violence. We must confess them, and as they are political (i.e. public) in nature, our confession must also be public. Let our opponents not have a single evil to hang over our heads, as we ourselves have put them there for the world to see. This is ultimately needed so as to avoid making the same mistakes again. There are five steps to the Sacrament of Penance:
We must do this as a society as well, and not be driven by pride.
Ultimately, as mentioned before, violence is a result of fallen human nature. So long as we live on this Earth over which the devil has dominion, we will suffer violence. Our objective as a society should be to work towards helping to diminish these acts of violence, these assaults on the dignity of Man, such that every man, woman, and child, from their conception until their natural death, may live a life in accordance to their innate human dignity, which all Men have, being made in the Image & Likeness of God.