Even in Herrera and Higgins study 25% of the time bear spray did not work. Herrera says "Pepper spray works, but don't bet your life on it." Would you trust your brakes if they didn't work 25% of the time? I know concealed carry permit holders will not trust a firearm that isn't 100% reliable.

And if you want to see how a firearm compares: https://www.youtube.com/watch?v=vUG8UPsgE3U (didn't even require a hit the muzzle blast and bullet hitting the water were enough which illustrates that firearms are often effective even without a hit), http://www.adn.com/alaska-news/article/twig-snap-alerts-dog-walker-charging-grizzly/2009/08/14/

Both of these incidents happened extremely quickly and both had positive outcomes with a handgun. There are more, lots more, but people believe what they want to believe, we're really good at self-deceit as a species.