A year later and still activating existential dread. Very well done.

Why is a bright future assumed?

in reality the graph alternates black and white and only holds true for one certain location/group at a time

Keeping in mind that a single axis for progress is reductive: also, don’t forget that there have been and will be backslides. For example, European colonialism set back a lot of progressive / alternative cultures, genociding them or converting them to something that better-served the interests of empire (e.g., race rules).