I believe sound retaliation is the proper course of action for any to take.
For instance, if they wouldn't go around randomly terrorizing people who are minding their own business and going about their daily lives, than they would likely have nothing to worry about.
Instead, they simply choose to piss on others way of living, of course their actions are going to warrant a lot of hate and desired revenge.
The thing that still bothers me is I can't even begin to understand why we(US) were training and helping them before all this. I would of assumed government learned their lesson down Bin Laden path, since we(US) were responsible for his training as well and look what it caused; but now it seemed like a great idea to give plenty of military teaching to an entire group who have similar religious views(or probably same) as Bin Laden.
Views that they aim to use and justify as a bloody crusade.
There is honestly no helping these people. These are people that use child soldiers, strap bombs to children, sell girls as sex slaves, and of course have no courtesy or care for proper warfare tactics given how they aim their assaults to civilians with their 'holy war.' These are people that thrive in warcrimes, if you can even classify them(ones responsible) as 'people' at all.
What really needs to be done is something to get the message across for them to settle down and leave people alone with their shenanigans.
I am sure a few carpet bombings would likely lead to their inevitable downfall, rip their city apart, but that in itself isn't one of the best moves as it will likely still catch and kill civilians.
I say pull a Black Jack Pershing
on the terrorists and see how well they may decide to keep up their behavior.