I believe we are all born seeking certain needs (mostly practical, but as we age and become more complex, our needs can become more complex and branch into the intellectual and emotional). You can pull ideas from Maslow, although not necessarily his entire pyramid structure as listed; but he details various needs humans can have.
We also have particular preferences on how to chase down those needs. [For example, Horney's "moving against," "moving towards," and "moving away" broad categories.] The preferred strategy can impact how one's motivations are perceived and what kind of damage or help can be offered, although it's still not necessarily good or evil.
For example, when you naturally move aggressively towards others, this can be to pursue them for good reason or to damage them as enemies. Moving towards another can be to manipulate them for your own desires or to bond a positive relationship. Moving away is perhaps the most neutral as it withdraws and limits its ability to help or hurt; however, you can hurt people by abandoning them, and you can help them by not pursuing them and invading their space. So these various styles more determine the type of power and influence you'll wield over others driven by your motivations.
But back to good vs evil. I tend to see morality in terms of "identity circle." Is your sense of self limited to just YOU, and thus all that you do is directed towards either benefiting yourself particularly or protecting yourself particularly? Or to what degree has your sense of self expanded to include others in to the circle of identity? (To put it another way, how wide is your embrace?) The wider the embrace, the more people you perceive as a unit of "you" versus "other" -- and thus you will protect and nourish people in your circle as you would yourself. This is most obvious with the broad-scale philanthropists who are essentially humanitarian in outlook... many are included under one's umbrella of "self."
Still, do we see to connect with the "other" and bring them into the fold, or do we seek to destroy the "other" to gain power?
I guess I think we're more neutral when born. We do have all these various individual settings in place, and yes there can be dispositions where we might be more cranky/aggressive versus more open/considerate by nature. I think it's kind of a "ball" centered around neutral and people can fall within the bounds of that ball... some more on the side of defeating others and some more on the side of embracing others... but environment/upbringing as well as experiences can move people in one direction or another even if that original preference lies intact somewhere.
I don't think anyone is particularly locked into 'good' or 'evil'. However, the more you move away from the "balance" point and approach one of those two limits, each is a gravity sink of sorts and I think it becomes harder and harder to pull away from it. It's like starting on a peak where the slope is relatively flat but becomes steeper as you move away from that flatter surface. So you can start walking down one side or the other, but then to get back to the other means climbing back up the hill you just went down. It's not impossible, but to overcome the wiring you've been burning into yourself over time, well, it takes more and more energy and more severe experiences to motivate you.