I don't believe that its always appropriate to love your enemies or turn your cheek. A person must use some judgment in determining how to respond to an opponent. Anger, ridicule, and even violence can be context appropriate responses. Those things are not off the table, but we seem to have forgotten that compassion is an available and attractive option. Also, escalation is easy. De-escalation, not so much.
Humanizing people is always worth doing, regardless. I can humanize Osama Bin Laden, but I still believe killing him was the best available course of action. Even in the case of someone that you might be inclined to denounce as evil, humanization is valuable. It's humbling, for starters. Even the Nazis were regular people. Had families and spent time with their children. Liked dogs. Experienced fear, and wanted to build a better world. These people were not "other", they were not intrinsically, necessarily immoral, as a group. They did not think of themselves as villains. They were as human as you, and when you absorb that it becomes a cautionary tale against what we are capable of doing to others when we believe that we are in the right.
In less extreme cases, our enemies may morph into mere opponents. Our opponents may further transform into people we disagree with only on specific issues. There is so much complexity in the world, in a culture, in each human being. We are not cardboard cutouts, or caricatures, or archetypes. We are not straw-people.
Many of our contentious interactions are religious or political. We're talking to Christians and Muslims and Atheists. We're talking to Republicans and Democrats and a whole spectrum of people who are disgusted with both. We're talking to people who are "anti-choice" or "anti-life", to "feminazis" and "rape-culture apologists". Probably we're just talking at them. I am not suggesting false balance here, nor condemning moral outrage or confrontation. I am saying that one or several problematic positions do not define a whole person, even if those positions are thoroughly awful, and that the possibility for redemption is always there.*
We are not able to dialogue with straw-people, because the scarecrow doesn't have a brain (no wonder he disagrees with me!) To have cooperation there must be a good-faith conversation with real people. We must acknowledge that we might be wrong, or that they might be wrong and still not be Hitler. We might both be wrong, or we may be disagreeing about a topic on which objective truth is difficult to access. Too often single points of disagreement lead to the stance that an opponent's entire character must be flawed. Cardboard cutouts are only useful at the shooting range.
A diplomat was asked: "Do you trust Iran?"
"I trust Iran to act in their own self-interest.", he replied.
This was not a slight, but a powerful statement about the nature of diplomacy. If we can find common interests, then we can find grounds for cooperation, even if you don't like me. Even competing companies, who supposedly treat their adversaries with gladiatorial ruthlessness, engage in coopetition. This is possible because it is in the best interest of both to do so, because many games are not zero-sum even among clear competitors. I have deep problems with the right-wing evangelical juggernaut that is Focus on the Family, but they and I both believe that reducing the backlog of children waiting for adoption is a worthwhile thing to do. We have common ground, and could potentially cooperate on that specific endeavor.
I think it's hyperbole to suggest that creating a wider sense of community is necessary. We can, and do, get along without it. We will probably survive as groups even if things come to bloodshed, and some of us don't survive as individuals. I do think that a wider sense of community is necessary to human flourishing, however. We have a choice here. It isn't between annihilation and utopia, but between a spectrum of possible conflict and a spectrum of possible cooperation. One of these choices is clearly better than the other. We virtually all want to be good, and do good, and experience good things. People simply disagree on what that means, and how best to get there. There may be limits to the common ground we can find without compromising personal principles, but a quick survey of the landscape tells me that our conversations are stopping far short of those borders.
Sometimes its just a question of what we choose to emphasize.
*Psychopaths are a special case, and one that I'm ignoring here.