It's about responsibility. Democrats belive the state has a reponsibility to take care of every aspect of your life, including your protection.
God forbid should you have a gun and be able to protect your own life or that of your family. To the Democrats (the statists), that is the responsibility of the state.
"There is nothing which I dread so much as a division of the republic into two great parties, each arranged under its leader, and concerting measures in opposition to each other. This, in my humble apprehension, is to be dreaded as the greatest political evil under our Constitution."
- John Adams