Ponder,

We have ample cases where pepper spray has been used against bears and human beings.

There have also been cases where human beings have used firearms in self-defense, and these are documented as well.

The subject at hand is "escaped murderers in national parks" as a threat potential for your visit to Yellowstone and so on.

If we take the class of people we're concerned with as
A. "escaped murderers" or the a sub-class within that set
B. "escaped murderers who kill others while escaped" or further refine that to
C. "escaped murderers who kill others while escaped and in national parks"

The decision factor here is if you consider scenario "C" as one that is of sufficient probability to warrant carrying a firearm or now.

You add to this risk assessment the threat level you see from aggressive wild animals, in particular bears and you then come up with a total threat level where you would consider a firearm a piece of gear worth the weight and size in your kit.

You then add in the utility of the tool against other threats you might face, including hunger or a need to signal others in an emergency.

In my threat assessment, scenario "C" is highly unlikely, however, threat levels from wild animals are higher, and the need to signal or obtain meat higher still. So in my assessment, "C" is one of the smallest factors that contributes to packing a firearm - but I do pack one because it's a versatile tool for more than one reason.