Car crashes are still responsible for a million deaths and something like a trillion dollars in damages every year. Reducing the number of people on the road with slowed reaction times would only have to make a very small relative dent in that to have a very large absolute effect.

On the other hand, toxoplasmosis treatment is almost certainly not the low-hanging fruit here - better cultural attitudes and vehicle safety features already make driving much safer in some places than in others, and self-driving cars may make the very concept of driver reaction time moot in a generation.