No, it's not pointless to do marginal things that could make marginal improvements. Regarding broken homes:
1) Is there are critical mass of experts and/or legislators who agree that "broken homes" contribute to gun violence? Maybe. I don't know. In any event, this is the first hurdle to get over.
2) Let's assume one gets over #1. Some problems are not complex, but STILL very hard to get effective legislation to address. "Fixing broken homes" is no doubt HUGELY, HUGELY complex. For a similar magnitude of (and related) challenge, see "Poverty" and "The War on Poverty." How's that turning out? A good supposed conservative like you should be awfully receptive to that point.
So, yeah, if and when one chooses to endeavor to get over the 2 freakin' Everest's above, it behooves one to ALSO in the meantime do some more marginal things (background checks, perhaps age restrictions, magazine capacity, bump stocks [already made illegal?], etc.).
Because guess what? As implied above, you ain't gonna fix "broken homes" ANYTIME soon......
I mean, we can't convince tens of millions of people in this country that having a malevolent autocrat wanna-be as president is a bad thing. Or that evil scientists and doctors and public officials weren't simply out to get them with COVID mitigations. Suppose we stand much of a chance of convincing lots of people to establish and maintain loving spousal relationships and raise their children well?
Sure, go ahead and try. Good luck.