Are we going to commit armed forces to an invasion of Yemen now that we've "discovered" that terrorist activities are originating there? Using this logic (the "Afghanistan Logic"), how many s**tbird countries are we willing to invade? Somehow, our leaders have decided that trying to kill off the source of this terrorism where it originates is the best policy to protect us here within our own borders. Maybe a serious reevaluation of this logic is called for. It's possible that it would be more effective to actively and throroughly police our own borders (sea, land and air) than using the needle in a haystack approach trying to root terrorists out of remote caves over hundreds of thousands of square miles. Even when we squash terrorist activity in a limited area, the terrorists draw back until we leave, then return and resume their activities (proven to be the case in Afghanistan).
In addition to policing our own borders effectively, we could use intelligence to make surgical strikes on known targets of high value, much like Israel did on Iraqi nuclear reactors. That ended Iraq's quest for the A-bomb. By sending large, conventional forces to flail and flounder around in the wilderness while the terrorists look on and laugh is expensive, stupid and ineffective.