As I understand you correctly, you are assuming carrying a large folding knife into Disneyland serves no purpose other than to cause a possible danger. I guess we can say that about a lot of things then. For example, the only purpose for high-performance running shoes in Disneyland would be for a person to run from security. That type of person is potentially dangerous to the kids. So, Disneyland had better prohibit high-performance running shoes. Walking shoes are sufficient for Disneyland.

As another example, Disneyland should make sure MMA fighters and similar athletes have a legitimate reason for being in the park. Their bodies are their weapons. Disneyland should only allow these athletes in the park if they can prove they are going to spend a significant amount of money. Otherwise, the risk of having their weapons in the park is unjustified.

Seriously, I have been carrying a relatively large folding knife for over twenty years. Never have I hurt anybody with my knife. Never have I thought about hurting anybody with my knife. It's a tool. It's not a bizarre tool either. I may have a need for this tool in Disneyland, as others have also pointed out above. Anyway, I should not need a reason. If carrying a knife is not outlawed by state or federal laws, then it's unnecessary for Disneyland to impose additional restrictions.

Last but not least, criminals will smuggle whatever weapons they want. Knives and other weapons are plentiful in prison, which is an environment that is way more controlled than Disneyland. Accordingly, even if Disneyland had a policy of not allowing knives, the policy would only regulate honest people and make the simple-minded people feel safer, while actually providing no additional safety whatsoever.