Because firearms are a Constitutional Right. Driving is not.... you do have the right to travel. But driving is not a right. The right to travel is.
By creating a licensing system (NYC) you can restrict those that you feel are socially undesirable to not be able to posse arms.
Firearm ownership ties into the right to keep and bear arms and also the right to self defense. By creating a licensing system, you will setup a situation that can be abused and controlled.
Nazi Germany did that, the Soviet Union did that, the People's Republic of China does that, Cuba does that, Venezuela does that, etc......
You can either live in a free and open society in which you have the rights that we all enjoy. The right to freedom of speech, the right of freedom of choice if religion, the right to keep and bear arms, the right to be secure on our persons and in our homes, the right to a fair trial, the right to not incriminate yourself, etc...
Or you can live in a secure society. Yeah you have safety but you have no freedoms. You will be safe because the government will go through your house when ever they want to check for "bad things". Criminals will not have guns because people that do have them will be arrested on the stop and never face trial. You won't have to worry about people screaming and cursing at each other because you will not have the freedom of speech. etc......
In the end, you can either live in a free and open society with rights or you can live in a closed and secure society with no rights. I will never trade my rights for security. Because sadly you cannot live in a free and open society with rights and be secure. It's one or the other.