* The current political climate, specifically the apparent (re)-rise of strong strains of nationalism, populism, and borderline (if not outright) fascism.
* Climate change
* The way technologies that nominally exist to further benevolent ends are bent to serve harmful ends. Take, for example, the use of the Internet to enable massive surveillance, and to distribute disinformation, as opposed to its more noble purpose as a way to enable "the global village", interconnect people, further scientific research and cultural sharing, etc.
* The constant lingering threat of nuclear war, or other man-made catastrophe (for example, a release of a human engineered virus that causes a pandemic like COVID, only worse)
etc.
And just to balance the equation, here's my answer to the other question "What makes you optimistic about the future?"