No, you're right.
One of the big issues in historical discussions, especially if you get out of scholarly material is that a lot of people do tend to have overly simplified views of conflicts and if they've got a side they are biased towards, the other side is demonized, as you have said.
In any conflict, especially war, the door is opened for vendettas and sociopathy and basically evil (chaos is a ladder). The Nationalists had Hitler and Mussolini as backers, the Republicans had Stalin. Of course, both sides (yes, both sides) had good people that were stuck in the middle of it for whatever reason.
Hemingway's account in the middle of For Whom the Bell Tolls where the rebels go into the town and murder priests and other supporters of the conservatives really struck me. Hemingway actually fought with the left and was sympathetic to them, but even he was aware of atrocities that were being committed by his own side.
The demonization of the other side and the inability to call out our own side when they're doing wrong really just weakens one's own cause. It's kind of sad that we as humans still haven't figured that out, but I guess it's something about how we are and it's a tragedy cause on that other side is just another person.