So much confusion about 'duty to retreat.'

Joshua is incorrect, as are a couple others. Somewhat disappointed in the writers of the Slate article too.
Here's the precise text of Florida's self-defense statute. Subsection (3) is the Stand Your Ground component:
http://www.leg.state.fl.us/statutes/index.cfm?App_mode=Display_Statute&URL=0700-0799/0776/Sections/0776.013.htmlHere's the deal: in American States without SYG, Canada, Britain, and IIRC Australia, (Common Law) the way self-defense works is thus: if confronted with force you reasonably believe will cause you death or grievous bodily harm, you may use force to prevent injury to yourself which is reasonable in the circumstances to prevent it so long as you use no more force than is necessary. That may include force you intend to cause death or grievous bodily harm to your assailant if it becomes necessary. Thus, the Common Law requirements for self defense do not actually include a duty to retreat physically, they require you to do everything other than kill the person unless it is absolutely necessary. That is what duty to retreat means - proportionality. If one can get away, then killing your assailant is unreasonable and not self-defense. If one can stop the assailant without killing them, then killing them in said circumstances is not self-defense. It means that use of deadly force is an absolute last resort.
Other European countries require proportionality - if someone tries to kill you, you can kill them back so long as the options you use are proportional to what was used against you.
In all of those situations, it effectively means that if you are confronted by someone who you believe intends to kill you, your legal obligation is to only kill them if you have no other option.
In Florida, the SYG law means that if someone confronts you in a manner which you believe is intended to kill you, you are allowed to kill them instead even if you had other options. It's a fundamentally flawed law; the point of 'duty to retreat'/proportionality is that 'intent to case death or grievous bodily harm' is a subjective notion - it's entirely premised on what the defender believes. Duty to retreat and/or proportionality are factored in because some people have unreasonable ideas of what constitutes a threat of death or grievous bodily harm. Removing that aspect of the Common Law principles of self-defense removes one of the protections that limits the use of self-defense to situations broader society is comfortable with.
The Florida law actually goes so far as to remove proportionality:
(3) A person who is not engaged in an unlawful activity and who is attacked in any other place where he or she has a right to be has no duty to retreat and has the right to stand his or her ground and meet force with force, including deadly force if he or she reasonably believes it is necessary to do so to prevent death or great bodily harm to himself or herself or another or to prevent the commission of a forcible felony.[/u]
The emphasized portion means that if you are in public, you aren't doing anything illegal, and someone commits or is about to commit a forcible felony that you observe, you can kill them if you believe it to be necessary to prevent that offence.
Check out what forcible felonies are in Florida:
Forcible felony.—"Forcible felony" means treason; murder; manslaughter; sexual battery; carjacking; home-invasion robbery; robbery; burglary; arson; kidnapping; aggravated assault; aggravated battery; aggravated stalking; aircraft piracy; unlawful throwing, placing, or discharging of a destructive device or bomb; and any other felony which involves the use or threat of physical force or violence against any individual.
How's that for scary? How many members of the gun-toting public do you think can tell the difference between aggravated assault and common assault? Common battery and aggravated battery? Robbery versus break and enter?
There are a lot of reasons Florida is OK with people killing other people for.