> What's to stop bad actors from fine tuning open weights to run fully automated genius-level scams personally targeting basically everybody?

You mean like ChatGPT hacking Hugging Face? Obviously nothing can stop the closed weights providers from doing "genius-level scams" and in addition you won't know how they did it and what models were used.

In short, only a good guy with open weights can stop the bad guys with closed weights, be them fine-tuned or pre-trained.