Answer:
They try to beat me, they try in vain. And when I win, I end the pain.
I cost no money to use, or conscious effort to take part of. And as far as you can see, there is nothing to me. But without me, you are dead.
My first is equality; my second is inferiority; my whole is superiority.
A house with two occupants, sometimes one, rarely three. Break the walls, eat the boarders, then throw away me.
I fly, yet I have no wings. I cry, yet I have no eyes. Darkness follows me. Lower light I never see.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?