According to the L.A. Times, the law allowing citizens concealed is bad because:

Opponents say the law ratchets up the potential for violence in parks, where for seven consecutive years rangers have been the most assaulted federal law enforcement officers, according to data compiled by the park service.

And

There were 1,844 weapons-related offenses reported in national parks last year.

Wait one minute. So Federal Agents have been regularly getting their butts kicked, assaulted and what-nots so it makes sense that the common citizen should be disarmed so we can get our butts kicked also? And not counting that guns were already in National Parks, just in the hands of those willing to break the law, you know? CRIMINALS.

Seriously people. If you wanna make a case, use logic before opening mouth.

For a more detail explanation of what the Law does or does not allow, check this great article by David Codrea.