How does Slaughterhouse 5 make relevant commentary on modern day warfare?

Vonnegut's persona of Billy Pilgrim witnesses the bombing of Dresden by the Allies in February of 1945. From the safety of a bunker beneath the city, the POWs can hear the destruction, but it's only when they are brought to ground level that they see Dresden has been obliterated. The impression Pilgrim and the others have is that earth now resembles the surface of the moon, completely barren and devoid of life.
This, then, is "modern warfare": total destruction. Vonnegut observes that Dresden had no significance as a military target. The bombing was carried out to demoralize the civilian population of Germany, or out of a desire for vengeance for the war crimes the Germans had carried out over the previous six years.
If modern warfare is total destruction and makes no distinction between the military and civilians, one needs to ask what it is that has caused this situation. Vonnegut does not, and it is not necessarily his place in a work of fiction to do so, provide the contextualization and analysis to explain it. Is it simply that technology has made weapons so advanced and effective that they inevitably will kill more people and destroy more property than in the past? Or is it that in the twentieth-century, even the side in a war whose cause is "justified" has become so amoral that it feels no guilt about carrying out the same level of destruction—albeit in retaliation—as the enemy? There are no definitive answers. One also has to remember that the destruction of Dresden was done with "conventional" weapons, incendiary bombs, just as were being used at the same time against Tokyo, six months before the atomic bombs were dropped on Hiroshima and Nagasaki.
Even a casual reader knowledgeable about World War II would probably observe that, in focusing on the personal story of Billy Pilgrim's reaction to this "total" modern warfare, Vonnegut seems to overstate the "guilt" of the Allies in prosecuting the war in this manner. Given the genocidal war the Nazis, and to some extent the Japanese as well, had perpetrated, the retaliatory measures cannot be understood without taking into account these war crimes committed by those who had started the conflict in the first place. Modern warfare, we can conclude from Vonnegut's narrative regardless of his lack of historical contextualization, is not simply fueled by technological advances. It has been an effort to punish the unprecedented war crimes of the modern age, resulting from the need of even governments with the best intentions to shorten war by demoralizing the enemy populations, as the Allies did in World War II.