More vetoes mean less action  The reason there are only a few states with veto power is to prevent most states from being able to block essential security action that is in the international interest.  More members increase the chances of vetoes and deadlock. There have been 263 vetoes since the founding of the UN with vetoes having been used by every permanent member. The veto is used to protect national interests not for the good of the international community. [1] States provide veto cover for censure against those they consider allies or even trading partners. Thus the most common veto in the last couple of decades has been by the USA to prevent censure of Israel. China and Russia on the other hand have prevented action against Syria and Sudan despite crises in these countries. [2]  Give more countries vetoes and it will be used more often. Even worse an African country would have very different interests so would be vetoing different proposals. Thus for example in the past the USSR and USA have vetoed the admission of new members from Angola to Vietnam. An African veto might be wielded to discourage secession movements by for example vetoing the membership of South Sudan.  [1] Okhovat, Sahar, ‘The United Nations Security Council: Its Veto Power and Its Reform’, Sydney University, CPACS Working Paper no.15/1, December 2011,  pp.11-12  [2] United Nations, ‘Security Council – Veto List’, Dag Hammarskskjöld Library, accessed 20/12/2013