Decapitation strikes require precise intelligence. We did try to kill Saddam Hussein during the initial stages of OIF, but we lacked intelligence (Cobra II provides a great overview of our failed senior leader targeting attempts during OIF). It is incredibly difficult to conduct these types of strikes and every time you miss your target becomes stronger and you become weaker. Don't forget we tried to take out Qhaddafi during the Reagan Administration. These were airstrikes - sending in SOF requires even better intelligence and access. We certainly don't have to conduct a large scale invasion or nation building to address these threats, but decapitation strikes require intelligence and intelligence takes a great deal of time and effort to build - we don't always have time, access, or resources to build the necessary intelligence. Additionally, many of the future threats to our nation will likely require conventional forces with superior ISR, targeting, mobility, and logistics. It is not difficult to imagine a scenario where we have to fight a conventional conflict. Although we likely won't face China on their ground or here at home, we certainly may be involved in a conventional conflict over scarce resources. It is impossible to predict the future and it is only wise and prudent to prepare for the threats which are most dangerous. To paraphrase Clausewitz, "War is more than a chameleon" - you really don't know what you are going to get once you pull the trigger.