The reason you're likely to be attacked in a bar is because people in bars get drunk, or at least intoxicated enough to have compromised judgment. People in bars with compromised judgment AND a firearm will of course proceed to attack with their firearm, turning what would otherwise be a completely survivable fistfight incident into a mass shooting with fatalities instead.
I realize that many people defending guns in bars will insist that a drunken lout with a gun would easily be subdued or killed by other, not-drunken louts (or drunken not-louts), i.e., good guys with guns, before he has a chance to wound or kill anyone, because they live in a TV-Rambo fantasyland; but that is not actually a realistic scenario.