We're not quite there technology-wise yet but that isn't the biggest issue. BEA Systems has flown its "Flying Test Bed" aircraft with no one at the controls (though there was someone on board just in case).

But as pointed out in a BBC article:

But while it is one thing to conduct test flights with pilots on hand in case of an emergency, it is quite another to pack 350 passengers on to plane and send them on their way across the Atlantic with no one at the front. As a result, autonomous flight technology is likely to be adopted in stages.