Nobody doubts that adding a master password will stop nobody who knows what they are doing. If someone has access to your computer and wants to do damage, they have full access to do it.

However, keep in mind 'open door' syndrome. A crime of opportunity is very different than one of bad intentions. Leave a car unlocked with a $20 bill on the seat and you might find that $20 gone when you return. Now, if you lock the doors the odds are it will still be there when you return. The fact is that when you increase the barrier to doing evil, many give it up. A potentially honest person might open a door and take something but if they must now break a window to accomplish the same task many will not pursue it.

Having to potentially download a third party program to decrypt the password DB and/or run additional commands is very different that just navigating to the chrome settings page. Its almost akin to why so many coworkers always jacked each others wallpaper when they forgot to lock their computer. They could have still done it even though the computer was locked, but they did not because it was too much work.

Also, going off what you have said, the "locking" process in windows is pointless since it offers a false sense of security. It can be broken just by rebooting the computer with a boot disk, right? So why include it? Because its useful.