Stand your ground is about duty to retreat.
Castle doctrine is different from Stand your Ground. Castle Doctrine provides the presumption that deadly force is justified if a shooting takes place in a qualifying occupied structure or space if the attacker has broken in or is attempting to break in. It may also provide some civil immunity for qualifying shootings. The presumption of justification can be attacked by the state if there is sufficient evidence to refute the presumption.
Basically Castle Doctrine shifts the burden of proof. In a "normal" self-defense case, the defendant must admit to committing homicide (or assault with a deadly weapon) and then prove to the state that the action was justified. That means that a defendant in a "normal" self-defense case has to admit to guilt and then starting from that position, prove that they are innocent. With Castle Doctrine, if the requirements are met, the state must prove that the use of deadly force was NOT justified and if they can not, they must presume that it was. Basically it puts defenders whose shootings meet the Castle Doctrine requirements back into the position of being innocent until proven guilty.
While many of us here understand, I also think it's important to educate people on what "homicide" is. Too many people equate homicide with murder and it causes confusion amongst the average layperson.
Homicide is the killing of another human being. No more, no less.
Homicide encompasses murder, voluntary manslaughter, involuntary manslaughter, and justifiable homicides like self-defense. Maybe a couple more, but this is it in a nutshell.
So while all murders are homicides, not all homicides are murder.
So for a defense which starts with admitting to homicide isn't an admission to murder. It's saying "yes, I killed this person". The defense to the killing of the person is "it was justifiable under the laws because (fill in the blank with the statutory exceptions for use of deadly force)".
The key is, as you say, you have to admit to the homicide in order to defend yourself. To say you DIDN'T commit homicide is to say "I didn't kill this person". If that's the case, then you cannot claim self-defense as a form of justifiable homicide later.
For states which have a form of castle doctrine, the burden shifts because, as you say, there's an initial presumption that a person who meets the "castle" part of the doctrine (they were in a place they were legally allowed to occupy, such as their house, home, vehicle, etc.) and therefore had a right to defend themselves, even to the point of deadly force, against someone else who was a credible threat to their life/limb.
A homicide was committed and it's upon the State, in this instance, to show that the threat was NOT credible enough to warrant the use of deadly force.
These are such touchy legal concepts to explain to some, especially those who are adamant against the use of deadly force for gun control purposes. But they are essential concepts to those who choose to carry/use firearms for the purpose of self-defense.
Ignorance of these legal principles is legally dangerous to people who may choose to defend themselves by any means, much less with firearms.
