Given how effective natural selection is for selecting surviving traits, why are you so sure that a parasite can't have some level of behaviour altering effects

Given how effective natural selection is for selecting surviving traits, why are you so sure that a parasite can't have some level of behaviour altering effects? Sure, it's probably not an inner monologue telling the hyena where to go, but it does appear that infected animals are either more reckless in general, or less cautious when faced with lions specifically - a behaviour which helps the parasite reproduce. Do you have any sources for your claim that that toxoplasmosis doesn't have any behaviour altering effects?