
This is new to me but might be useful nowadays
kakistocraThcy (n.)
1829, “government by the worst element of a society,” coined on analogy of its opposite, aristocracy, from Greek kakistos “worst,” superlative of kakos “bad” (which perhaps is related to the general IE word for “defecate;” see caco-) + -cracy.

As soon as I saw your post heading I remembered an old delight of mine: “Never underestimate the power of fools in large numbers…” π