People were pretty sick of fighting the war at the time. Just about everyone who wasn’t a national higher-up just wanted to say, the hell with it, let’s go home.
I don’t know if killing a bunch of POWs is going to strengthen resolve on the Allied side - especially when the POWs are American, latecomers to the war - enough to demand unconditional surrender from the Central Powers.
However, given that the POWs are American, the wrinkles in the US will be more drastic - I’m just not sure which way.
Door number one is that Congress’ postwar way of thinking - basically “the hell with internationalism; we’re going to do us and Europe can fuck off and go away” - becomes MORE pronounced. This probably means a more insular culture in the 1920s and 1930s, but overall there won’t be that much long-term change. Japan is still itching for resources and territory, their leadership still swallows the crazy pills, and unless some switch flips in Japanese leadership and they decide to attack the Russians instead, WWII goes more or less like OTL.
Door number two is that “Remember the POWs” becomes a massive rallying cry and Congress gives more leeway to Wilson in regard to the League of Nations. I don’t imagine it does a lot to deter the Japanese, but it may put the brakes more on the Germans. The sanctions on them probably trend more toward “break their backs and make them rebuild slowly and sanely” and less “keep them down just enough to piss them off and get King Batshit into the top office.” So WWII doesn’t happen as we know it, the US goes heads-up against Japan, and they decide, you know what, Europe may be a bunch of lunatics, but we can shape Asia into our own image. This probably means the KMT plays to at least a draw in the Chinese Civil War, and the Korean War is either a success or leaves a smaller DPRK rump state that probably doesn’t last.
Europe, however, ends up like a bunch of squabbling cousins fighting over Grandpa’s estate and never gets around to the whole European Union thing, and the Soviets agitate in Europe but don’t really do the whole Iron Curtain.