I've come across this question multiple times.  I've seen it being asked by people in the aftermath of natural disasters like the Indian Ocean Tsunami, after man-made disasters like 9/11, etc.  The question being that how could God allow this to happen?  There is bewilderment as to how God could just stand by and allow such large-scale loss of human life, as happened in the Tsunami.  People wonder how God can be so cruel as to allow such complete and utter destruction of human life and cause such misery for years to follow for their kids and relatives that survive. For some people, the Tsunami was a great injustice and the fact that it happened, made them question God and wonder if God existed at all.

Personally, I don't think its a question of whether God is powerful enough to stop all of this or not.  When one talks of "injustices," one is talking about "injustice" as perceived by us.  When people die, of course other people are saddened about it, especially if they were very close to them.  It would be a gross injustice to you, but should God consider that an "injustice?"  Death/destruction and creation are two sides of the same coin.  So, should God seek to become subjective and dwell upon each individual human life and think about the "injustice" (as perceived by humans) before taking that life away?

I believe God has to be objective and see things above and far removed from how most humans see things.  Stars are born and are destroyed and so are planets.  Perhaps, the Earth would be destroyed one day too - by an asteroid perhaps, by our own foolishness through nuclear weapons perhaps.  So, we all have to die one day.  Perhaps, an alien seeing Earth being destroyed would wonder about what an "injustice" it was to see billions of humans being wiped out in an instant.

In answer to the question, I would say that we shouldn't expect God to be intervening in our day-to-day lives.  Injustices in the world are a fact of life and I don't think there would ever come a day when there would be no injustices at all in the world.  I don't think injustices are a feature unique to Earth or humans.  I am sure if there are other alien societies in alien worlds, injustices would exist there as well.  Its just a fact of life and I think we should just accept it - rather than question God each time we perceive an "injustice."