I think Danny is correct, profiling has its place, and it is already being done in certain ways in certain places as a number of drug dealers have found to their cost.
Personaly I think the most effective security tool is a brief interview. Going into Canada a year or three ago, I was asked four extremely searching questions in about thirty seconds by their immigration guy and there was no way I could have answered them if I wasn't who I said I was and preparing to do what I was going to do. These guys were sharp.
In answer to all those who say "Well I got my leatherman into the cockpit", "I can get airside at XXX without going through security blah blah" and similar statements pedalling the fallacy that because screening is never 100 percent effective that it ought to be abandoned, you need to understand the military concept of "Defence in Depth".
The concept of Defence in Depth implies that you never rely 100 percent on one single resource to protect you. Instead you use a series of interlocking resources that overlap in such a way that there is always another layer of defence if the first is breached.
The five most obvous layers are locked and strengthened cockpit doors, sky marshalls, screening and removal of sharps, xraying of baggage and security background checks on all staff. That last item is being inflicted on the entire Aviation community in Australia as we speak.
There are other layers that may exist but I don't wish to speculate.