McNamara Fallacy and its Applicability

You are overthinking it.  It is a classic non sequitur.  Just substitute car deaths for gun violence and to see it.

McNamara Fallacy

The syllogism of the question can be presented as:

If the numbers on gun violence speak for themselves, then we should ban guns in the country!"

The numbers on gun violence speak for themselves.

We should ban guns in the country!"

OTOH, it can be presented as:

Since the numbers on gun violence speak for themselves, we should ban guns in the country!"

The former is making a reasoned statement that leaves open the possibility that the numbers on gun violence do not speak for themselves.

The latter, which more accurately re-presents the original question's example

"The numbers on gun violence speak for themselves, then we should ban guns in the country!"

includes an axiom, a assertion that is self-evident to the speaker but not to everyone. Indeed, putting a still-finer point on it, the axiom is ambiguous, since the gun opponent hears the fear in the same phrase that the gun supporter hears the need for teaching.

The further discussion also engages in a variant of the same fallacy, along with an excuse for some people's ownership of guns, which I've seen in this argument against ownership before.  The idea that some people hunt with them and some just show and sell them is a Strawman Fallacy that allows an assertion that there are more important reasons to ban than to continue to permit.

Then, the argument continues into Appeal to Fear , then uses it to do its own form of McNamara ("These deaths are more than statistics.") reiterating explicitly the appeal to fear.

I can't tell if this was simply a question about the applicability of the McNamara Fallacy, as it seemed to start as, or a clever way to present the author's ideas as if they were only a matter of analysis, while actually "backing into" gun-banning as a proposal.  On the off-chance of the latter, I will add my response.

Guns are dangerous, but 12 yo's have handled them safely since there've been 12 yo's and guns, using gun control.

Guns are also for hunting and targets and trading and display and, and... but the primary value is for protection against a tyrannical government.  The option is not given to remove that protection, nor is it granted by our constitution, which merely recounts gun-keeping and -bearing among the rights that are inherent to humans.

"The numbers on gun violence Do NOT speak for themselves. We should NOT ban guns in the country!"

But is this really more important than gun violence, specifically deaths? 

Importance is not a factor in the fallacy. The fallacy is defined as

When a decision is based solely on quantitative observations (i.e., metrics, hard data, statistics) and all qualitative factors are ignored.

In examples, I get to dictate intent for the purpose of illustration. In that example, the speaker has ignored all qualitative factors, including the qualitative factors supported by the statistics.

In reviewing this definition, I would propose a change (this was defined in a academic text from 1970). Suggesting that "all" qualitative factors are ignored might make an impossible standard. This is fallacious because qualitative factors are not given due consideration. In other words, it is not a binary fallacy but one on a continuum of fallaciousness like most informal fallacies.