Even Germans believe today that Germany was the bad guy of WW2, the things that happened under Hitler were so mind boggling and awful that no sane person could help but say that violently removing him from power was important, but WW2 might have never happened in if WW1 never shook out like it did, and as an American I'm kind of curious if we had some moral reason to fight in WW1 or if it just sorta happened? I don't know enough about the war to say we swung it, probably helped to have a massive injection of manpower, but I know even just before WW2 "European politics is none of our business" was a very popular position in America. So was there some good reason to get involved from a wider human perspective like in WW2 or was it just countries playing politics. If I were an American in 1914 watching the war unfold would I be able to point to something to say "ah, that's why X is the bad guys in this war"?
Choosing a "bad guy" in wars is really subjective because most of the time it's never so black-and-white and clear when it comes to who has the moral superiority and justification over the other, but WW2 was an exception given the genocide tactics and aggression employed by the Nazis, which is pretty much universally condemned as immoral etc. That being said, your "bad guy" in WW1 would depend which side you were on.
For Germans, their "bad guy" was the British navy that had decided to economically blockade Germany and starve the country from food imports. Meanwhile the British viewed the Germans as war-mongers who invaded neutral countries like Belgium and torpedoed passenger ships. So here you have two different perspectives. There was also heavy wartime atrocity propaganda, like the "Rape of Belgium" that alleged the German army murdered Belgian civilians in droves and crucified captured soldiers, all of which was an exaggeration meant to demonize the German side as barbaric.
Objectively speaking, the Ottomans were the most immoral belligerent in WW1 because they committed the Armenian genocide for nationalist reasons and religious hatred/supremacy. Genocide, collective guilt, and targeting of civilians, guilty of association only because they belong to a particular ethnicity, is universally condemned as immoral.
From an American perspective during WW1, you would be exposed to news reports of Ottoman atrocities against Christian ethnicities and fundraising campaigns from the American Committee for Relief in the Near East (founded in 1915) to bring aid to Armenian refugees. So if you were a religious Christian, or anyone with empathy, you would sympathize with the Armenians and view the Ottomans as the "bad guys".
Also as an American, you would hear of passenger ships full of American civilians like the Lusitania being torpedoed by German U-boats, along with the Germans occupying and invading countries. Germany was portrayed as the enemy of peace, and as an authoritarian state later on when the Hidenburg-Ludendorff military government was set-up. So this was more or less the same perspective as the British and French regarding the Germans.