I would tend to agree, but you could just say violence may be going down in overall terms of sheer carnage but at the same time, you could also say we haven't had a big war in a long time, nor have we had any major conflicts of anger or diversity. The cold war didn't happen because of mutually assured destruction, and since then we've had no conflicts to comare to. But if WWIII walks around the corner and 2 or 3 billion people die within the span of 2 months, talk sessions like that will be considered laughably incorrect.
Thinking about WWII, it was bad yes, but it was also clean. Instead of 50,000 men lining up and shooting at each other for 2 hours until you can't take a step without landing on some part of someone, we had groups of thousands going about quickly and in, for the better part, moderately unpopulated landscapes. Not to mention most of the casualties were civilian as a cause of war crimes and indirect bombing and shelling.
I think the key of the degreation of violences in warfare is the advancement of technology and the lack of anyone to use it on. During the expansion of the Romans, so to say, armies of 10,000 men were needed to conquer cities and then, those men viewed the enemy, civilian or otherwise, and lesser beings. That, combined with a desensitisation from violence from the close, personal and extremely violent types of combat(Compared to today, shooting someone with an M16 at 500 feet is less violent than hacking someone up with a short sword) created a free-flow of violence which was transfered back and forth between soldiers and the people they conquered. That in turn created lasting images of horror and violence, mixed with anger, on the survivors.
There is the link between conflict and general society. A few hundred years ago, violence and war were commonly very close to home. Battlefields never existed across oceans or massive landscapes because Armies couldn't move that far. Today, there hasn't been any kind of direct conflict on American soil(Or most other countries) in 60 years, less so for other countries, more so for some. As society became less and less intertwined by war, due to it being farther away, people were generally less constricted by the visions of war and were free to focus on something else.