That’s sort-of a nonsequitor, because the incentives and practical considerations around slavery are very different from those around guns.

One of the chief questions is - is your government strong enough to actually prevent people from importing black market firearms in notable numbers?  Some governments are, such as Japan and the UK, which are both islands.  Some governments have large numbers of historical firearms that could not all be removed, and lengthy borders, such as the US.

If you can’t reasonably get enough firearms out, then gun control looks worse.  If you can, then it looks better.

The presence of firearms acts as a force multiplier for criminal activity, but also for civilian defense, however the key elements of gun-based combat center around cover, movement, surprise, and so on, so attacking is easier than defending.  This isn’t a total wash, but the effects are unclear.  It also offers the opportunity for a decentralization of power and probably makes what conflicts do erupt more likely to end in death.

A lot of this also depends on what’s meant by “gun control,” for instance banning fully-automatic weapons vs all handguns.

Actually, let me just link the SSC on this: http://slatestarcodex.com/2016/01/06/guns-and-states/

One of the things Scott points out is that we kill as many people per capita in this country without guns as the Europeans do in total, before we even add in the murders with guns.