I don’t understand how anyone can hate a stranger. 

Hating requires a lot of energy. I don’t think anyone is worth the energy of hate. Dislike or even be indifferent, but don’t hate. It’s not worth the toll it takes on you.

If you must hate (which of course is not an imperative), funnel that energy toward someone you know, someone who presumably has given you reason to feel so strongly negative.

But don’t hate a stranger. Don’t hate people you don’t know just because they look different than you or think differently than you or in any other way differ from you.
If you do hate strangers, I urge you to stop. I also want you to consider what you gain from this hatred and what outcomes you desire from the objects of your hatred.

Do you gain peace, health, or longevity from hating strangers? I’m certain you do not. 

And what about those strangers that you hate? Do you expect them to feel your superiority and cower at your presence? I’m certain they do not.

I most often feel pity and confusion when I’m the object of stranger hate.

And confused is how I’m feeling right now. Why hate me without knowing me? Why expend so much negative energy on someone who might be willing to be your greatest ally and friend?