It seems like some people are mixing up a lot of different self-defense concepts with the Castle Doctrine.
The duty to retreat is different from the Castle Doctrine, and not directly related. There was no common law duty to retreat, and many states have never had it. Even if places where there is a duty to retreat, that usually does not apply to the person's dwelling.
As I understand it, the Castle Doctrine basically does not allow prosecutors and juries to second-guess the use of deadly force in your own home. Under the common law, you could only use deadly force in self-defense when you reasonably believed that such force was necessary to protect yourself from the imminent use of unlawful lethal force by another person. That was the rule whether you were at home or at Wal-Mart. So if the jury could second guess you on any of those issues. For instance, if the burglar only had a bat, the jury could say that you were not threatened with deadly force. Or they could buy think that the burglar didn't want to hurt anybody, he just wanted to steal some bread and that you should have known that. Or that the burglar was retreating when you shot him, and therefore the threat was no longer imminent. The Castle Doctrine basically says that when someone breaks into your house, you can kill them. You don't have to prove that your use of force was reasonable, or that you were threatened with deadly force, or that what you did was necessary, or that the threat was imminent. No one is going to second guess you in your house.
Castle Doctrine laws usually have immunity from civil liability as well.
Relaxing the standards for self-defense in your car or at work may be good ideas, but they are really something else than the Castle Doctrine. Shooting a shoplifter in a convenience store is not an application of the Castle Doctrine. Texas lets you shoot people who are stealing your property at night; that is not the Castle Doctrine either. The media meme wants to portray all questionable self-defense shooting as resulting from the Castle Doctrine. We should resist this.