I'm referring to the '80s because that was when I was residing in Massachusetts, and that was what I could look forward to if I used lethal force in self-defense. Also an automatic 1st degree murder trial, "Let the jury sort it out" was the AG's idea of prosecutorial discretion.
As for the Wisconson case you're referring to, the facts not surprisingly paint a very different picture. Per this news item: http://fox6now.com/2012/05/05/photos-of-bo-morrison-crime-sc... and others, the porch was only technically one, it was fully enclosed and furnished like an interior room, had an appliance (fridge/freezer?) and other indoor style stuff, and critically, from looking at the outside, it appears to be fully a part of the house. I say critically because the outdoor pictures make it very clear this can be legitimately scored as a home invasion, whatever friends and family of the deceased propagandize.
And per this from the shooter's wife, "[she] told investigators she heard her husband say, “What are you doing in my house” twice, then “Stay where you are” twice, and later a single shot was fired."
So only "weak", no duty to retreat (in 46 states) Castle Doctrine comes into play. He was not shot out of the blue or from behind, there was a confrontation, so as long as the couple have proper account of the story and the authorities don't catch them lying the failure to prosecute looks like its solid. Just like the Zimmerman/Martin was before it become a political show trial.
ADDED: Not surprisingly for a state that was until that year solid Blue, Wisconsin as of 2010 didn't have a strong Castle Doctrine, the case law explicitly says "The doctrine is for defensive and not offensive purposes."
When you hear "unbelievable" stories like this, you should be suspicious, they're generally unbelievable because they're flatly not true, except in the sense of Revolutionary Truth, which as techies we shouldn't approve of (our computers do not care about politics, just that 1 + 1 = 010).