The Evil trait describes someone who is cartoonishly, mustache-twirlingly Eeeeeeeviiiiil!
The mitigating factor is the trait. So yes, they're 'evil', as a result of factors even more out of their control than someone with a fucked up childhood. Doesn't mean you can let 'em do the shit they want to, but it does mean that blaming them for it or trying to berate them for it, or even say they're bad people, is pointless. The first two would accomplish nothing, and the third is redundant.
And no, I don't call people evil. That isn't, in fact, necessary. Usually, I work on a scale of 'asshole' versus 'nice guy'. At the extremes, 'would and/or does commit genocide/ethnic cleansing', up to 'jumps on a grenade to save civilian lives'. I describe what they do that is good or bad, or both. Because that's what I have access to. I'm not omniscient, so I don't call people evil. If I was, I wouldn't call them evil. Suicide bombers believe they're martyrs, as do their comrades.
And this is leaving aside the fact that there's multiple ways to interpret morality, the most common two as far as I'm aware being Deontologism and Consequentialism. I'm somewhere between the two, like I'm guessing a lot of people are. Some people have morality given to them by their religion and/or imprinted philosophy. That's how they were taught, how they grew up, how they were indoctrinated, whatever you wanna say. Morality is very rarely objective, and when it is, it's mostly shit like 'punching people in the face for no reason'.
Objective quandaries don't show up in real life precisely because they're objective, so no one does them. If it seems like someone does, it's probably because of other issues, like being very impulsive. We all have that tiny part of the brain that says "I wonder what would happen if I just grabbed the wheel out of their hands and pulled really hard" or "What if I smashed the window on this plane out, right now?". We also have the much larger part that says "Well, people could easily die, so we ain't doin' that."