Essayist: It would be wrong to defend current testing procedures for new medications simply by appealing to the fact that test subjects are volunteers who are both apprised of and compensated for the risks involved.
Conclusion
It's wrong to defend current testing procedures for new meds on the grounds that the test subjects are volunteers who are warned of risks and compensated for the risks.
rephrase even though the volunteer subjects are warned of risks and compensated for them, these testing procedures for new meds might not be ok.
Evidence
It can be wrong to pay people to do something when they're under duress.
Evaluate
Once we eliminate the concession and rephrase the conclusion, the argument boils down to, because .
The author must be assuming that some of these test subjects who volunteer to participate in the test are choosing to do so under duress.
(There is some common sense behind this assumption. A lot of people who sign up for medical trials of new drugs are at a desperate stage of a terminal illness; other treatments have failed them, so they are trying this new drug under the duress of it being their only hope.)
Goal
The author is Assuming Applicability, i.e. assuming that the premise about would apply to the conclusion about .
So let's look for an answer getting at the assumption that these subjects are under duress when they choose to sign up for these medication tests.