Well, I suppose, if one wants to take that line, the "underlying issue" for domestic abuse is misogyny and patriarchy. And the 'underlying issue' for shootings is the wider culture of violence, and, specifically, gun-fetishism. Maybe could expand it to inequality and capitalism while you were at it. But I don't see much hope or inclination to address such 'underlying issues', so arguably, restrictions on guns (which clearly keep the death toll down in other countries) is the most practical approach.