Bad trips' are an ever-present possibility.
Informed consent is biologically impossible.
One can't grasp, in advance, the nature of the sorts of experience to which one is nominally consenting. Trapped in the squalid psychochemical ghetto of Darwinian life, we lack the necessary wetware to conceptualise radically altered states. We haven't even names for the strange new modes of selfhood and introspection their metabolic pathways disclose. Alas, pure reasoning is impotent to access their nature. This is because it lacks the semantic primitives with which to do so.