Why no assasinations?

What's with this taboo on assasination that the US government seems to have?  Why is it such a bad idea to send a covert unit to kill the leader of your enemies instead of carpet bombing the whole damn country, causing the deaths of hundreads of troops and civillians and costing billions of dollars? 

Assasination is a fuck good idea!  Why discount it in whole?

It's sad that this topic turned to this only over my use of the word "genocide." I used the word genocide to describe the modern wars because they usually amount to that after a country has been carpet-bombed for a year and then bought by corporations soon after. A common intent of genocide is not to extinct the peoples (Hitler) but their culture or their common belief. (soviet purges)

What the US is doing in Iraq is genocide against those who oppose the idea of their country being occupied and manipulated by a foreign nation. The people who believe that are terrorists, and according to the US terrorists are basically meat which must be imprisoned unconditionally until broken or blown up by a missile. If that isn't genocide of the true Iraqi citizen defending their country, what is?

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And as for this, God I hope so. Maybe in the future, just maybe, the politicians will be responsible for their actions and not civilian bystanders.