The ICC doesn't ensure stability. Instead, it makes sure war crimes are prosecuted only after they happen. The court has no authority to issue warrants before the fact. The only way the ICC is a valuable tool for stability is if possible war crimes deter potential dictators. By the time power-hungry people achieve their goals, it is probably too late for them to be concerned about being prosecuted by the ICC.
The court has so far only brought prosecutions against Africans. This creates the impression that the court administers justice selectively, and is biased against Africans. As a result the African Union is asking the court to delay cases against Kenya's president and deputy president until they are out of office. The perception of bias on the part of the court has resulted in increased instability and opposition to dispute resolution through the court on the part of African countries.