When you have more people going through a cp with no legit reason to be there then the incidence of everything goes up; wait times, and theft are no exception.
As a previous poster noted, it was not too long ago that it was allowed and at that time, pick pockets ran the trains at DEN and made a lot of people miserable.
Another poster noted that an automated authentication system would benefit the process, this is a logistical nightmare. It would have to tie into all the airlines ticketing systems and they are not uniform with each other. Then there is the issue of down time and who is going to pay for it.
You can get into the secure area if you can prove to the carrier that you have a valid reason. That is where it needs to be. The whole issue of checking validity of id is paramount in security because if you have a fake identification then you should be looked at closer because those people that are carriers of good i.d. have nothing to hide and those that are faking it are faking it for a reason. It doesn't mean that you cant fly.