rwl, that is true, some innocents would certainly be executed.  

However, innocents are dying now, so would the situation be better or worse?  Unless we put more than 11,000 innocents to death a year (the number of innocents killed by guns in 2013, excluding suicides), we still end up ahead.  Think about that for a moment.

FastStats: Mortality - All firearm deaths. Centers for Disease Control and Prevention. https://www.cdc.gov/nchs/fastats/homicide.htm (accessed July 27, 2015).