@Rava: If someone is pumping lethal gases into the air in your city and people are dying left and right, I assume you agree that it is the responsibility of the tzibur to shut it down.
Will you say, “If you’re scared of lethal gas, go buy yourself a gas mask and wear it constantly”?
I don’t think so.
Now, I’m not sure if guns are the same. Is owning a gun a definite prevention of gun violence? That is up for debate. I don’t know the answer.
But you can’t make a blanket statement that any time a person could theoretically help himself (especially if much effort, money, skill and inconvenience are involved), the tzibur is not obligated to get rid of the danger.