> I am arguing that not what the intent was originally for - it's a side effect that can help, but wasn't considered.
And I'm saying the intent doesn't matter, the side effect does. Let's say one group A say eating brain of fallen foes is good, gives strength, group B say, don't eat humans - that angers gods.
Group A eats some fallen foes, and by chance contracts prion disease and dies out.
Group B isn't going to think yeah, this was caused by microscopic particles. They are going to think - See. I was right. Gods are angry at you. Then they will persist to replicate the behavior for centuries after it could make any impact.
> I feel like that's a huge leap for what an STI can do.
It was an example. Since it already affects the brain, it could just evolve to make you more likely to engage in risky behavior and not use condom (like giving you an allergic reaction when using latex). Right now, it doesn't have this ability. But can we be certain it won't acquire it in future? We know at least one pathogen that can alter behavior in mammals (Toxoplasmosis).
It's better ofc, to eradicate it now and not worry about it, but the thing is, promiscuous behavior will always be a breeding lab for these kind of pathogens. Even if none exist, some might evolve into it. If there is a niche to be exploited, some pathogen will evolve to exploit it.