It is not a question of whether to respond or not — you can't help but react emotionally to violent schisms in the social fabric. But the question is how to respond.
First you need to decide how you wish to respond as a individual; as a member of society. This in itself is no small feat. Silence feels like implicit acceptance. Railing against injustice with words, although cathartic, seems like an empty gesture, especially from those of us not directly in the "line of fire" so to speak. So, action. But what action? The options, from silent protests to direct confrontation, all have their pros and cons, which it is up to the individual to decide between. Ultimately, few if any reach a completely satisfactory balance between appropriate scale without breaching the moral boundaries of the actor. (Violence as a response to injustice does not breed justice. Or simply put: two wrongs do not make a right.)
But if you are writer, or some other form of artist, words (or your medium of choice) are your primary weapon. It just feels wrong to write cheerful poems that ignore the storm outside the door. Silence may be implicit acceptance, but changing the subject feels downright complicit.
However, more often than not, art that attempts to address immediate political or social upheaval often falls flat. And the more pervasive and violent the upheaval, the less successful the art tends to be.
I am reminded of this fact by Juan Felipe Herrera's poem on poets.org about the latest police shooting of a black citizen. The poem is clearly heart-felt and well-meaning. More importantly, coming from the current U.S. poet laureate, it probably will have more of an impact than work by any other poet. However, the impact comes from the poem's context, not from the art of the poem itself.
It's not Herrera's fault. It is simply hard for a work of art to address horrific events of such scope and depth. Attempting to encompass the scale of the issue within a poem tends to result in abstractions and generalizations, that make the poem flabby; trite rather than touching, stereotyped rather than transformative.
But the artist has no choice but to try. And it strikes me that there are two options that tend to have a higher record of success than others. To encompass the horror without being consumed by its incomprehensible size, the artist needs to take the poem to an even higher, almost mythic level. Think of Robert Bly's Teeth-Mother Naked at Last, for example. The other option is to drive the poem deeply and inexorably towards the personal, to bring the issue down to size. An example of this is James Dickey's The Firebombing.
By personal I mean individual in scale, not personal as we tend think of art, as self-absorbed. In Dickey's case, he forces us to empathize with the bomber, not the victims, creating an uncomfortable union where we as audience must experience the separation and dehumanization needed to carry out acts of war. Another more recent example is Ross Gay's excellent poem about Eric Garner. This time, Gay focuses in flat objective language on the absolutely trivial, most human, aspects of the victim. The small but essential things that have been snuffed out, rather than attempt to capture the man as a whole.
An aside: part of what makes Picasso's Guernica such a remarkable work of art is that it some how manages to approach a horrific event from both a mythic and deeply personal point of view at the same time.
So what happens if you don't write about it? Well, that might be considered the third option. If you choose not to write about what is happening around you, and continue with the other parts of your life and art, something strange happens. You might be in the middle of a poem about the Edo period in Japan and its attitude towards western intrusions. Or might be writing about how the light at dusk filters through the leaves to form ever-changing patterns on your living room wall. And suddenly the writing takes a dark and ominous turn. Subjects come up you didn't expect. Your writing is hijacked by an emotion that demands to be heard.
Essentially, whatever emotions you do not address, start to seep into your work, ooze out of your pores, and inform everything you do. This might not be recognizable by anyone else. But as an author, you immediately detect the loss of control, the invasion of another, more influential consciousness on your work. Will it help? will it impact others? Unlikely. But it is the consequence of not taking action earlier. Or even writing a bad poem rather than no poem at all, when situations demand it.
As an artist, you may not be able to sway society, to influence for the common good, or change the course of nature. But then again, maybe you can. Maybe if you stop being an artist for a few minutes and just be a citizen, a member of society, a human being. Maybe what you say will have an impact. No more nor less than any other human. But collectively, as a voice quiet and firm, demanding that we, as a whole, act on our better, if sometimes flawed and susceptible, nature.