Well, it's been tried. In a country where people have guns, it's not a good idea. That's why Hitler, Stalin, Mao and others made disarming the people their number one priority.
“The most foolish mistake we could possibly make would be to allow the subject races to possess arms. History shows that all conquerors who have allowed their subject races to carry arms have prepared their own downfall by so doing. Indeed, I would go so far as to say that the supply of arms to the underdogs is a sine qua non for the overthrow of any sovereignty. So let’s not have any native militia or native police. German troops alone will bear the sole responsibility for the maintenance of law and order throughout the occupied Russian territories, and a system of military strong-points must be evolved to cover the entire occupied country.” --Adolf Hitler, dinner talk on April 11, 1942, quoted in Hitler's Table Talk 1941-44: His Private Conversations, Second Edition (1973), Pg. 425-426. Translated by Norman Cameron and R. H. Stevens. Introduced and with a new preface by H. R. Trevor-Roper. The original German papers were known as Bormann-Vermerke.
Regulations Against Jews' Possession of Weapons
Jews (§5 of the First Regulations of the German Citizenship Law of 14 November 1935, Reichsgesetzblatt I, p. 1333) are prohibited from acquiring, possessing, and carrying firearms and ammunition, as well as truncheons or stabbing weapons. Those now possessing weapons and ammunition are at once to turn them over to the local police authority. ... Firearms and ammunition found in a Jew's possession will be forfeited to the government without compensation.
Berlin, 11 November 1938
Minister of the Interior
Frick
As Nazi Minister of Propaganda Joseph Goebbels insightfully put it: “The Fuhrer is deeply religous, though completely anti-Christian. He views Christianity as a symptom of decay. Rightly so. It is a branch of the Jewish race... Both [Judaism and Christianity] have no point of contact to the animal element, and thus, in the end, they will be destroyed.”
It was clear that by the end of the war, Catholicism and anything else smacking of Christianity were next on the list. And though critics say that Germany before Nazism had tough gun laws, Hitler and his minions appeared in the streets with them on numerous occasions and, when captured, Hitler was only temporarily confined. You didn't see anyone except Nazis with guns after they came to power. But the Jews in the Warsaw Ghetto managed to get their hands on a few handguns, and they terrorized the Germans with them, who they picked off in small numbers of one or two at a time.
Bottom line: If you're going to outlaw religion, you better get the guns, knives and other weapons out of the hands of those who might fight back.