Why do people reject science and believe online conspiracy theories? How are people radicalized online and go on to commit acts of violence? Why is our society so politically polarized? Astonishingly irrational ideas are spreading. Covid denial persists in the face of overwhelming evidence. Anti-vaxxers compromise public health. Conspiracy thinking hijacks minds and incites mob violence. Toxic partisanship is cleaving nations, And climate denial has pushed our planet to the brink. Meanwhile, American Nazis march openly in the streets, and Flat Earth theory is back. What the heck is going on? Why is all this happening, and why now? More important, what can we do about it?  In Mental Immunity, Andy Norman shows that these phenomena share a root cause. We live in a time when the so-called “right to your opinion” is thought to trump our responsibilities. The resulting ethos effectively compromises mental immune systems, allowing “mind parasites” to overrun them. Conspiracy theories,