My personal belief is that it's not meaningfully true or false to talk about human nature, as if we can simplify the complexity of contextual behavior into a single boolean variable.

At various points, I have believed that human nature tends towards the bad. As I've gotten older, I realize that people sometimes behave in good ways in bad situations; they sometimes behave poorly in situations where it would be easy to do the right thing. The same person could do both, within a 10 minute span. Heck, I even believe that people's behaviors would change if the simulation could be rewound and replayed.

Human interaction is so complex. If you expect me to behave poorly because you're in a bad mood right now, and I live down to your expectations, how should we interpret it? I don't believe it says anything generalizable about either of our natures - we could simply be having a series of bad days that makes it more difficult to act nobly.

If one of your key beliefs so colors your view of your fellow humans, it's probably a very limiting belief. For me, I don't think there's much value or truth in predisposing myself to negativity by projecting it forward. Especially when there's no real benefit to doing so.