Regarding the arrest.
Generally I feel like people who do illegal drugs or even legal ones voluntarily take the risk knowingly.
So to me this is a legal liability issue for providing a safe experience to the user with due care of risks. Unless the providers acted with negligence or intent etc. Who knows the whole story, or how careful they were being.
That said TONS of people die from medical procedures and pharmaceuticals all the time. And people also die at amusement parks, pools, and skydiving. Especially if the person didnt share their medical history or other drugs they are on. But you need to prove that there was intent or negligence to do a manslaughter case.
With regard to toad venom trips. In a way I'm happy to hear that this came from him trying to help people and not an intentional violent assault type thing. I personally believe there is value in psychedelics. Not so sure about the toad venom angle specifically though.