Backing up the argument:
Targeted assassinations send terrorists the message that if they target others, they will become targets themselves. By assassinating terrorist leaders, many lives are saved. Israel prefers to arrest terrorists, but if it is impossible (which it is when terrorists hide among civilians in densely-populated areas), then Israel has no other choice but to defend itself against those seeking to murder its citizens.
Individuals who directly take part in hostilities cannot then claim immunity from attack or protection as innocent civilians. A terrorist who plans bombings and ambushes is considered a combatant until hostilities come to an end, and is therefore a legitimate military target.
The most common criticism of "targeted killings" is that they do no good because they perpetuate a "cycle of violence" whereby the terrorists seek revenge. This is not a compelling argument against the policy, because the people who blow themselves up to become "martyrs" can always find a justification for their actions. They are determined to bomb the Jews out of the Middle East and will not stop until their goal is achieved.
As long as the Palestinian Authority does nothing to stop the terrorist attacks, Israel has no choice but to act to prevent them, including by means of targeted counter-terrorism operations.
In terrorist organizations such as Hamas and Islamic Jihad, there is no true division between the so-called political arm and the military arm - leaders from all parts of the organization are actively involved in ordering and planning terrorist attacks, and, therefore, are combatants and legitimate military targets.
Under international law and the laws of war, it is entirely legal to target and kill an enemy combatant who has not surrendered. Palestinian terrorists are undoubtedly enemy combatants, regardless of whether they wear military uniforms or civilian clothing. It is lawful to target a combatant even if he is sleeping, so long as he has not surrendered. Indeed, this is similar to the way the US captured Saddam Hussein.
In the period of relative quiet that has ensued since the Palestinian elections, the Israeli government announced that it will abandon its policy of targeted assassinations for as long as the terrorist attacks do not continue.
Under any reasonable standard, Israel’s policy of targeted assassinations of “ticking-bomb terrorists” does not deserve the kind of condemnation it is receiving, especially in comparison with other nations and groups whose legal actions are far less proportionate to the dangers they face.
( See background )