Cosplay is a serious art to many people, and as such the props it requires can be difficult to re-create. Unfortunately, this can result in some cosplays that are a tad too realistic.
Normally, fake weapons brought to a convention like this are “peace-bonded” to mark them as fake, that way no one has to worry about anyone getting hurt. Real weapons are confiscated until the person owning them leaves.
According to Sign On San Diego, SDCC 11 has had quite a few real weapons show up at the convention center, including two machetes, a dagger, a K-bar knife, and an actual AR-15 rifle.
I’m all for good cosplay, but bringing legitimate weapons to a convention center just makes you look like a dingus.