Paganism is about honoring the fundamental aspects of authentic human experience. It’s about looking at the parts of existence that are terrifying and overwhelming and trying to figure out what they mean: things like birth, death, sex, war, love, art, and even the powerful, capricious, and unpredictable forces of the natural world. The gods give rise to these essential facets of human experience (and/or are themselves born from them), and to deny one or more of the gods because there is no place in your life or your worldview or your schema for the things they represent is to deny a fundamental part of who you are.
War is a part of being human. It may be ugly, brutal, and horrifying, but it is omnipresent. To be truly human is to know war. To reject Ares because you reject war is to reject a part of what it means to be you. And to reject Ares because you reject war means also rejecting warlike aspects of many of the other gods as well: Athena, Aphrodite, Zeus, Dionyus just off the top of my head.
Who would Ares be without war? A god of mental conflict? A god of physical exertion? We already have those gods. Ares is a god of a lot of things, and there are a lot of lenses through which to view Ares, but he is primarily a god of war. Trying to edit the war out of Ares is like trying to edit the sex out of Aphrodite. I don’t know what you’re left with, but it isn’t the real deal. That kind of selective approach to the gods is apparently pretty popular among neopagans, but I honestly don’t think it’s a road that is going to take you anywhere worth being.
Think about it: the soldier knows both war and peace, but the pacifist tries to know only peace. The pacifist is rejecting an entire part of human existence because it does not suit him or her. Whether that’s a thing worth doing, or a thing we should be doing, is not actually the issue. But I would maintain that trying to edit human existence to remove the bits we don’t like is just not what any kind of real paganism is about. Christianity does that, with its vision of a new heaven and a new earth. Not paganism.
I also don’t think, with regards to Ares, that it’s a question of whether violence is necessary or justified, but merely whether it is an essential facet of human existence. Violence IS. War IS. We can play at quasi-Christianity if we want and imagine a utopia where violence no longer exists, but even in Christianity that requires massive divine intervention. The overwhelming, unanimous weight of human history tells us in no uncertain terms and with no exceptions that war and violence are fundamentally a part of the human condition.
Whether or not this reality is morally acceptable is a question that is, in my opinion, not even on paganism’s radar. Violence is a part of human reality, and paganism is about how we honor and respond to human reality. The ethics of paganism ask not whether a violent society is morally acceptable, but instead ask “given that violence and war exist as a part of the human condition, how do you respond virtuously?”
Look to the epics, the philosophers, and the myths. Look to the maxims. Tell me what the answer is. The world is violent–we honor that when we honor Ares. The question is how you respond with virtue when presented with that violence, whether you’re a kid in the hall at school getting beaten up by bullies, a young man who just got his draft notice, or a parent whose family is threatened.