Q. I heard that Horav Miller Shlit'a opposes carrying a gun on Shabbat, even on places where there is a valid safety concern, I don't understand, doesn't Sakanat Nefashot, or the danger to life supersede other Torah prohibition? How about when walking to shul Friday night in Mexico City?
A. Historically, there were occasions when even in New York some permitted carrying weapons on Shabbos and of course it is common in Israel in Yeshuvim exposed or close to the border or Arab settlements.
Horav Shlomo Miller's Shlit'a opinion is that, if someone is concerned for his safety or survival, he should preferably stay at home and don't go to shul carrying a gun, especially in locations where there is no Eruv.
As I'm personally familiar with the situation in the south. The advise is, that one may preferably hire affordable security guards to walk him to shul and back, as is already common there.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit'a