The injustice would be governments that let dozens of millions of people die every year due to something that has a cure available.
This is more of a sidepoint, but...
It is possible you will die soon and I could prevent this by putting time, money, and effort into improving your health. It is possible, yet if I don't do so, I am not negligent in my duties, I am not treating you unjustly. If I do choose to help you, that is going above and beyond, that is postively a "good deed".
But if I don't any resources of my own to help you, and decide to point a gun at someone else and compel them to give over some of their labor/resources to take care of you with, that IS injustice. In fact, that is a form of slavery.