Ordinarily, liberty and security conflict, so we have to give up one to get the other. Today, ours is a freer and safer nation. All law-abiding citizens should rejoice. As for the criminals, they will need to think twice before preying.
Addendum: It will be said that today's ruling constitutes judicial activism. It is nothing of the sort. The five justices in the majority engaged in standard legal reasoning. All they did is incorporate the Second Amendment, i.e., make it applicable to the states via the 14th Amendment. Most of the rights set forth in the Bill of Rights, such as the right to speak and the right to exercise one's religion, have long since been incorporated.
Addendum 2: As usual, Clarence Thomas nails it.