Because it is the ultimate civilized act. You may not use force against me without a very real risk of being shot down. If you approach as a brute, intending to force your way upon me, you will probably die.
So you must interact with me as a civilized man.
If you seriously have to ask this question, then you are either very poorly informed about today’s society, very, very insulated and protected, or just plain stupid...Maybe all of the above...
You remind me of what Bernard Goetz said; “If someone tries to impose their will on you and you have a gun then they have a problem.”
Yes, it is. A firearm is the difference between a society wherein brute force rules and one wherein it doesn't. That is a change in the human condition so fundamental it shocks me that people can ignore it.
Now and then someone will bleat "Imagine a world without guns." And you can, it's easy. Ghengis Khan.