The fallacy in your argument is the straw man that anyone here is suggesting that EVERYONE, or at least every non-felon, needs to engage in concealed carry. No one has suggested that, and it is not necessary. You just need enough sheepdogs among the sheep to make thugs think they might end up like Trayvon.
For more on the general idea, go find the famous sheep / sheepdog essay on firearms carry.
Here, I did it for you, Alex
On Sheep, Wolves, and Sheepdogs
By LTC (RET) Dave Grossman, author of “On Killing.”
http://mwkworks.com/onsheepwolvesandsheepdogs.html
Another good way to look at shall issue CCW is as a mine field. Without it there’s a whole mass of open fields with innocent sheep mindlessly grazing that can be taken by predators at will. Adopt shall issue CCW and the whole landscape becomes a mine field for those same predators; hence, far fewer predators.