Does the pattern of armed robberies at daylight correlate with the pattern of gun ownership across the US, or no?
If not, the causality may be a lot more complicated. People don't turn into gangsters just by owning more guns. As you mention, USA is the most armed country in the world, which means that Latin American countries have, theoretically, fewer guns than the US. But they have a lot more gang violence, so much more that LatAm cities fill the "top 50 violent cities in the world" category, with barely any representants from the Old World (AFAIK only Johannesburg is up to par).
The same people arguing about violent crime in the USA could do themselves a huge favor by being open to more gun control, but by and large, they are against it.
Oh, there are multiple reasons for gun violence in the US (in decreasing importance from easy access to guns). Replace "gun control" with anything that might reduce it and this statement is still probably true.
If not, the causality may be a lot more complicated. People don't turn into gangsters just by owning more guns. As you mention, USA is the most armed country in the world, which means that Latin American countries have, theoretically, fewer guns than the US. But they have a lot more gang violence, so much more that LatAm cities fill the "top 50 violent cities in the world" category, with barely any representants from the Old World (AFAIK only Johannesburg is up to par).