> A third of the entire human population is infected with toxoplasmosis, in some places nearly every human.

So if it is often harmful to some extent in people who do not show severe symptoms, then it is a terrible disease that causes widespread harm. There is evidence it causes lesser, but possibly significant harm, in far more people than is generally recognised:

https://pmc.ncbi.nlm.nih.gov/articles/PMC2526142/