Not sure if it was mentioned previously but the whole bag check was done out of appeasing the public after 9/11. Disney management knew that is was not "effective" security countermeasures, but due to customer complaints about a lack of security it was put in place. It serves merely as a deterrent.
Anyone that works in the security/law enforcement/counter terrorism could point out countless flaws in that system (employees are not screened, no metal detectors, free access to resorts/monorails, no screenings for vehicles, etc). But, it gives people a sense of security and that is a big thing. If someone wanted to do something bad, they don't have to do it in a park, but merely in the proximity of Disney (heck if they did something at a
Disney store in Iowa, the headlines would just display "disney").