Individual nations should have the right to police themselves without a court miles away interfering. If African nations abuse their own citizens and the rest of the world is unhappy about it there are many other ways to show displeasure such as sanctions, withdrawal of financial aid, abandonment of that country by tourists etc. Of course these measures harm those who are already oppressed rather than the petty dictators who are considering withdrawal from the ICC (with obvious self interest). 

These nations may withdraw, as is their right but don't be fooled by the smoke screen of racism they give as a reason.  And don't be swayed by bleeding hearts that want to continually send money and support that just lines the pockets of these dictators and lets them stay in power. Things will get much worse before the people revolt and it gets better but progress must come from within.. 

Maybe the real war criminals are the bankers who look after the money these dictators steal.