I personally think this is a big mistake. The national parks have a concentration of both wildlife and tourist. I think we will see not only wildlife being "accidentally" but people to. I can just image John Doe who's never handled a weapon thinking I'd better buy a gun to protect my family on our trip to bear country in Yellowstone. Then the first time something stirs in the brush he gets scared shoots and you have one dead tourist innocently shot because they where in the brush taking a picture of a flower.
Now don't get me wrong, I am all for the freedom of right to carry a weapon but I think allowing them in our National Parks is just a recipe for a disaster. I've also got personal experience with this. I've been shot at 3 times and hit once. All of them in the woods on our farm. The idiot that shot me was illegally trespassing on our property trying to shoot a deer. I guess I looked like one.

Heck I'm the kind of idiot that probably does need a gun in the parks. I love to go alone into the back country to shoot my pics. I move as quiet as possible and hope to see a bear. But, while it will suck if Mr. Grizzly eats me it's my own fault. What right do I have to act that like that in the animals domain and then shoot it because I'm dumb?