Why not “genocide”?
In our society, we have detectives who investigate a crime, lawyers who prosecute the offenders and judges who sentence them. If a crime is in progress, we call the police; we are not expected to stop it ourselves—unless it’s genocide. This is the distinction that the Genocide Convention makes, in its very first article:
Article 1
The Contracting Parties confirm that genocide, whether committed in time of peace or in time of war, is a crime under international law which they undertake to prevent and to punish.
Simply defining a crime does not compel action by third parties. The Genocide Convention does. (This is essentially the “Good Samaritan” law in the Seinfeld finale.)
The reason governments don’t want to recognize Darfur as genocide is because they would then be required, by law, to intervene. I believe that intervention would otherwise be illegal without a UN Security Council resolution.
Now, if we had a proper international police force and not just the ICC, things might be different.
That’s my understanding of the situation, anyway.