[These are thoughts from a sleepy brain. I hope they are not too abstract to be convincing or useful.]
To love people, you must first see people. If you cannot see people as people--or rather, as persons--then deep compassion will be impossible.
It is difficult to recognize another person's personhood. The other person is all wrapped up, in clothes and flesh, in attitudes and posture, in language and culture. Maybe the other person thinks in radically unfamiliar ways, and so acts in ways that are unpredictable to you, and therefore disturbing.
Otherness tempts us to judgment. It is easy to look out from the familiar windows of my own perspective, and think that I see the world outside me as it really is. The Other outside doesn't make sense, seen through my lenses, except as rude or deceptive or stupid or lazy or cold. It is easy to look out my windows, forget the glass is there, even forget the frame is there, and think: what I see is what is. I see that person, and he looks deceptive to me: he is deceptive.
But the windows are there, and they are made of imperfect glass. It is dirty, or streaked from being imperfectly cleaned, or between its double panes it holds a film of water vapor mixed with dust. Or the glass itself is lumpy, or curved, or contains bubbles. Moreover, the frame is there, limiting the extent to which I can see even a distorted view of the Outside and the Others who inhabit the Outside. The frame, the walls, the windows themselves all limit the accuracy and completeness of the view from inside. And so as long as I stand inside, looking through the glass, I will never see the Outside as it actually is. I need to step outside and look directly at the people around me and the world around me if I want to actually see them.
Compassion is the thing that opens the door and enables me to step outside. Compassion comes from knowing or trusting that that Other being is a Person, exactly the way that I am a Person--no more and no less. Without putting faith in the Other's Personhood, it is extremely difficult for me to have compassion for them. I need to see (with the eyes of faith) that the Other has a story, a mind, a heart; a language, an experience, a culture; thoughts, feelings, memories; a soul. Then I can humble myself to imagine their perspective, and to guess at their motivations with a charitable attitude. Then I can have compassion. Then I can begin to love.
[Credit: I first encountered the idea of personhood or Christian personalism in Thomas Merton's Seasons of Celebration, which I very much recommend.]