On one hand, a gun is an object with an intended purpose. In this case, the purpose is (objectively) to kill. The same can be said for bows and swords, for example, although the latter two lack in 'efficiency' when it comes to the damage they can do within a set period of time.
Indisputably, guns are more lethal than swords or bows, but not illegal in the U.S. for identical reasons (these reasons being hobbyism and sportsmanship). I'm personally not citing the second amendment because, in theory, the government is far too well-armed in both the aspects of physical weaponry and intelligence to be overthrown by loosely-organised local militias - although I completely understand the ethical value in preserving the individual in the face of tyranny and the wish to keep weaponry, even if it is just as a quasi-political statement.
Ethically, the issue is complicated. Let's approach it from a utilitarian perspective, i.e. 'trying to achieve the maximum good for the maximum number of people'.
I've been digging through some statistics and came across this, featured in the BBC (2016 article, data from 2012)
This shows me two things:
a.) Homicides in the U.S. are incredibly high in comparison to the other three countries.
b.) The majority of these homicides are committed using guns.
This, however, hasn't fully convinced me that making guns illegal won't cause at least a significant part of these murders to be committed using other tools. Besides that, simply comparing the non-gun homicides already shows a unusually large discrepancy when comparing the figures. Does anyone else have any data to support or deny this? How do we know the United States has a 'gun problem' and not a 'homicide problem'? I personally feel very conflicted on this issue.