As others have pointed out, you can't just take passwords from the Keychain even with the user logged in. It's much more difficult than what you're imagining. I'll refer you to this article:
http://bit.ly/JA0fhQ.
But returning to your original comment, you're suggesting that the encrypted Keychain is just as insecure as Safari storing your passwords in plain text. That's simply not true. To steal passwords stored in plain text, I can use any method that gives me access to your hard drive - no password required at all.
You, however, are arguing that if I'm currently logged into my account, then you can access my Keychain passwords. Let's pretend that's true for a moment. If someone gets access to your computer while it's logged in, of course you can't count on the security features; that's really a no brainer. Instead of trying to read your Keychain, an attacker can just open a browser and navigate to any site that keeps you logged in or autofills your password. Why steal the keys when the vault is already open?
But assuming you practice good information security, you would obviously logout or lock your computer before leaving it unattended. Then an attacker may still be able to read anything stored in plain text, but they would have no practical way of accessing your Keychain. It's not "open" in any sense as you suggested.