Agreed.
He was a petty thug...
Agreed, as I've said. How many times do I have to repeat myself on that?
However, the one aspect you are overlooking is that he was the petty thug fighting bin-Laden's buddies. The Northern Alliance may not be a shining model of the democratic process, but would it make sense for us to start bombing them too?
Once you consider relative transportation infrastructures, Afghanistan is far enough away from anything we give a damn about--the Balkans are RIGHT NEXT to the Mediterranean and Europe, two areas that we DO care about.