I apologize for taking this off-topic, everyone, but as someone who has spent a large part of my life around the live music business, I've kind of reached my breaking point with the ticket stub/re-entry bit. I'm going to say my piece and you can take it or leave it, but it would be great if the thread could stop focusing on it and blaming folks who have done nothing wrong, and instead figure out what happened to Morgan.
For starters, you're seriously underestimating the "sneak" factor of a lot of people. I could easily send a friend into the building to see one band, meet them between sets, take his or her ticket and go to the security staff saying, "Please, I'm a girl and I'm all by myself and I didn't know any better!" There are very good reasons that the policy is in place and has been in place for years (if not decades) at just about any venue you can find. If you start making exceptions for one person because they're alone, and one because they're female, and one because they made a mistake, you basically need to toss the rule and allow anyone and everyone into the building if they can show you someone's ticket stub. It is a business if you're the band or the promoter or the venue, and you have to protect your own interests - you can't sell a fifty-dollar ticket and have three people get inside with it. It may sound cold in light of what's happened to Morgan, which is a terrible tragedy, but it will not (and frankly should not) change.
Aside from people "sharing" a ticket simply to see a band, I could go inside to deal drugs for the first hour or bootleg one band's set and then sell my ticket to someone and go on my merry way having profited twice or more from it all. I could get kicked out for being violent or overintoxicated or trying to sneak backstage and either re-enter if I could find a new gate where they don't recognize me or sell my ticket to someone else who could enter freely. None of those things are right and many of them will jeopordize the one aspect of safety that the show is responsible for, which is that of the paying patrons who are in the building.
Finally, and I don't wish to blame Morgan's disappearance on anyone other than who abducted and harmed her, she was an adult as are most other people at concerts, and as such she was responsible to know the rules and follow them. I've left a show once myself after an arguement with a friend. I did not expect anyone to let me back in because I cooled down and wanted to see the concert, nor should they have let me in if I asked. Asking people to look out for one another to the extent that they're able is one thing; asking people to babysit other adults is another thing entirely. It sounds to me like Morgan understood this herself as well, since she apparently tried to re-enter, was refused, and let it go. What happened to her after that is the part we should be focusing on.