Safety is compromised when traveling and entering the national parks.  If you have a concealed carry permit, when entering a national park, you must make you weapon legal to proceed into the park.  This means you must stop prior to entering a national park, unload, and store your weapon and after you leave, making you carry gun ready again.  This may alarm someone who may be passing by and seeing this activity.  As I am sure, someone has already stated.  Hiker, anglers, and others travel the parks alone.  Remote as most parks are rangers and police cannot protect you and may take hours to get to you if they are alerted to trouble.  There are so many reasons to allow carry I will let others comment.