Why is that true today, but wasn't true the many times some group in the US did medical experiments on some vulnerable population without a complete disclosure let alone consent?
Things go through institutional review boards now that are concerned with such past failures.
I admire your trust in other people.
Do you have a better solution?
Yes, don't perform medical experiments on people who can't consent, and loudly object when someone suggests anything that sounds like it.
That is what informed consent is designed to achieve. What you want people already thought about and tried to implement in a realistic way to achieve those goals.
Would you like to hear about treatment of prisoners in early middle age Europe?
There is no reason to assume that.
The US currently inters tens of thousands of people without access to family or legal counsel.
Are we currently experimenting on these prisoners like the imperial japanese army? The answer is absolutely not.