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?

Uhh Saddam wasn't the problem? Isn't that painfully clear considering we're at war with THE COUNTRY WE'RE SAVING. He had absolutely nothing to do with the solution.

As for Venezuela: HE IS EVIL BECAUSE HE WONT LET US ASSFUCK HIS OIL SUPPLY.

Anyway, we've had a hand in many assassinations since the 50s. Believe it or not, buddy, we go to wars with countries, not governments. This isn't the middleages, we don't have Kingly scuffles and grudges, we simply commit genocide. The war has been with the people ever since democracy started up.