From my vantage point it looks like you have to literally be selling fake dietary supplements on the back of a conspiracy theory about the Sandy Hook kids being crisis actors to get yourself kicked off Facebook.
> According to Facebook’s policy, it does not allow ads promoting sales of firearms, silencers, other weapons like knives and fireworks, and ads promoting the brandishing of firearms.
Guns are not only legal, but Constitutionally protected. What explanation for banning them other than pushing a Democratic pro-gun-control agenda? Imagine the furor if Facebook banned ads for contraception or abortion services.
It absolutely is a free speech issue. It's not a First Amendment issue, but First Amendment issues are only a subset of free speech issues.