Yet Another Reason to Fear Accurate Gun Use Research.

It seems that there was a study published in the Western Journal of Medicine back in 2001 that came up with these results:

RESULTS AND CONCLUSIONS

Even after many of the firearm victimization reports were excluded, the data show that more survey respondents report having been threatened or intimidated with a gun than having used a gun for self-protection. Most judges rated the reported self-defense gun uses as probably illegal in most cases, even assuming that the respondent had a permit to own and carry the gun and that the respondent had described the event honestly. Guns are used to threaten and intimidate more often than they are used in self-defense. Most self-reported self-defense gun uses may be illegal and against the interests of society.

Results like that don't look too good for the "pro-gun" side.  That might also be a reason for the "Get Away with Murder" laws since it doesn't look too good to have a legal inquiry into these matters if most cases of "self-defence" may be illegal and against the interests of society.
Much better to say "I wuz actin' in sef-deefence" and end the inquiry in that case.
See:

Are guns used more by US civilians for self-defense or for intimidation? West J Med. Jun 2001; 174(6): 396.