I don't follow your argument. This isn't just about leaving your computer unattended and unlocked (of course you should lock your computer whenever you walk away from it).
Let's say someone steals my laptop. It's running Linux, and sadly Chrome doesn't support this "experiment" in Linux yet.
The attacker doesn't know my password, but they can use a live CD to mount the filesystem and reset the password to "hello".
Then they log into my account, open Chrome and are able to immediately view all stored passwords in plain text. This could have been prevented by having a master password.
How is that a "false sense of security"?