Now don't put words in my mouth :0 I do not believe in the broad concept of 'the ends justify the means'.

What I do believe in is that if you are going to make the conscious decision to mobilize your population to kill a group of others, then it is in your interests to achieve victory as quickly and with as few losses for your population as possible.

Killing civilian populations have worked to achieve political objectives. You can look back to the Khans who killed entire towns to be a lesson to other towns to not resist or Allies who firebombed, Americans in Linebacker II. In each of these cases they had some success in achieving their political objectives.

IF I were OBL I would also engage in terrorism if I were commited to using war to achieve my political objectives. There really is no other rational options as he does not have the support of a state; which means he can not wage a conventional war.