Well, one has to be extra-careful in this situation. The general (UN Security Council) rule of thumb is the international community should only act when a government's bad actions end up being a threat to neighbouring nations (this was the entire claim behind WMD in Iraq). Sometimes, due to the balance of world politics, getting the UN to move on a particular government can be fraught with difficulty. I have little problem, for example, with the Vietnamese government (acting against China and the US) deciding to invade Cambodia to remove Pol Pot - his regime was causing spillover effects into Vietnam and Laos (and Thailand for that matter).

In general however a dictatorial government is best overthrown by the people who have lived under it.