I could imagine that in practice you end up with a bunch of vulnerable people submitting themselves to experimentation by powerful companies, which is an unhealthy dynamic.
Beyond that, allowing for these experimental trials, regardless of their success or failure, can accelerate medical progress that can enable better care for many more people in the future.
It's so strange that people feel it's wrong for patients to make their own choice on this, but they are okay forcing others to not have treatment. It's a "My decision is better than yours, I can decide what is better for you.