With all due kavod l'torah, it appears some rabbanim are having the same issue as one rabbi had with the rally. Specifically, in that case, as I understand it, the main objections that formed the basis of it being prohibited were (i) a pastor speaking at the rally, and (ii) hatikvah being sung.
Was a single yeshiva bochur going to leave the rally, throw his black hat off, cross himself, and then run to buy the biography of Ben Gurion? I think not. That concern, BH, is as abstract as it is anachronistic, and fortunately, as far as the bnei yeshiva are concerned, it has been relegated to the dustbin of history.
Similar to the objection to the rally -- where it appears certain rabbanim may be trapped in the past and utterly unaware of the true battles of the present which need to be fought -- it seems that other rabbanim are also tragically unaware of current state of affairs when it comes to owning a weapon.
Take as a recent, if not perfect, example of what happened yesterday in Yerushalayim. Two Israelis with guns eliminated two evil murderers. Now I'll readily admit that (i) it was Israel, and not America, where the Rabbanim conceded it may be allowed, but America has become much more dangerous place than I think either of them recognize, and (ii) an innocent person with a gun was killed by friendly fire.
But can anyone seriously contend that had they not had those weapons, the casualties would have not been five, ten, or even twenty times worse what they were?
No one is (or at least should be) suggesting that everyone with a social security number and a heartbeat should be carrying a weapon -- into shul or otherwise. Everyone should have minimum required training to own a gun and for those who wish to carry inside of shul, where there could be 100s of protectees flitting about, the training should be 50x more. And I know where I live that is the case.
To dismiss with a broad stroke the entire notion of owning a gun because of a personal anecdote demonstrating that guns are dangerous lacks nuance and, I believe, an understanding of facts on the ground.