Well, just to play devil's advocate, I don't get patted down leaving the airport, so I'm not terribly sure that your point about baggage theft is relevant...
If I see someone holding a laptop I don't immediately think "crime", if I see someone holding a gun...
There's a big difference between looking for certain objects that are banned, and looking for objects that are perfectly allowed but might be in the hands of someone other than the owner.
It's like having a bank, where the front door is policed by an army, but the backdoor is wide open for employees, and every window in the place is open every day.
Given the amount of theft from airport bags, and hence stolen goods _leaving_ the airport, do you think it's any harder to bring illicit stuff in?