A number of posters do seem to be making (unwarranted IMHO) assumptions of the purpose of the CC on the flight deck. I believe the primary purposes of the CC are to (a) alert the pilot who is currently absent if the flying pilot becomes ill or in any other way erratic and (b) open the sodding door so that the other pilot can enter.
There has been speculation that the flying pilot might disable the CC but given the pilot will be strapped in (at least initially) I think the only way that could easily happen would be by means of a gun which is a different bag of worms.
Will this proposal solve the problem completely? NO! It is however comparatively easy to implement, from the airline's point of view does not increase crew costs although there may well be some increased costs for training.
Very smart post. I have operated with this policy for many years. It was introduced by my opeartor to address incapacitation and door operation issues. In the case of the GermanWings crash, had the policy been in place, it possibly would not have stopped the event occurring, but it certainly would be one more issue for the FO to deal with (assuming the reports are correct). In this respect, a deterrent policy, although not intended as that.