Pro: Political leaders typically have powers that ordinary citizens do not have. When those powers include the capability of ordering the oppression, torture, or killing of innocent people, and when leaders exercise those powers and no legal means taken by any party are effective in preventing the extreme abuses of authority, and when killing the offending ruler(s) will prevent further grave injustices, and when such killing is the only way to accomplish that objective, then assassination is justified.
Con: Leaders rarely act alone or without at least the tacit support of several others, so that the elimination of one leader may do little to change the unjust policies of a government. Assassination is often simply ineffective in making the desired social or political changes.
Pro: Assassination, even if ineffective in producing desired social or political changes, nevertheless can have a great symbolic value. In particular, it can bring into prominence the cause(s) championed by those who align themselves with the assassins.
Con: Assassination can be counterproductive, for the assassinated leader could become a martyr. The killing could generate great sorrow and anger in the followers of the assassinated leader. The assassination of Aquino in the Phillippines in 1983 failed to eliminate opposition to the regime of Ferdinand Marcos. Indeed, it galvanized that opposition, which then managed to take the dictator out of power.
Pro: In a world where some nations or groups within nations plot and carry out assassinations, other nations need to consider assassination as one of the possible means by which to defend themselves. For assassination can disrupt the operations of enemies to the state.
Reply: Replacements for assassinated leaders come quickly when the cause for which those leaders fought has widespread support among a large number of people. Assassination removes a leader, but it can rarely remove the reasons why the leader emerged in the first place. Brave, ambitious people are often willing to fill a power vacuum.
Pro: A nation that accepts assassination as an option in its policies deters its enemies from attacking it.