I agree with you in that consistent behavior builds habit and character. That works on an individual level, and with a large system of incentives and some social rules, can also affect large chunks of society.

But when I talk about human nature here, I'm referring to the deep traits of humanity that repeatedly show back at all times in history. There was greed when Socrates was alive, there is greed to day and I forecast that there will be greed 2000 years in the future. And that will happen with greed, with love, with hate, with envy, ...

Not that what I think about the future of humanity matters much though, we won't be there to see it.