In the world of medical research, ethicists say it is unethical to pay a substantial amount of money to research participants. If you give a hefty sum for participation, people might sign up for risky research that they would otherwise avoid, so they can only receive minimal compensation for their time. Large payments exploit them and violate their autonomy by removing their ability to refuse participation. Of course, people with little money and few resources will sign up for risky experiments, anyway, because they need the money, even if the sum is paltry. Poverty reduces one’s autonomy and makes one ripe for exploitation, unfortunately.
The other way to look at it, of course, is that individuals are participating in research that may yield lucrative products, may cause unpleasant or harmful side effects, and may be quite inconvenient, indeed. For loaning their bodies to this unpredictable, but likely profitable, enterprise, it might make sense to compensate them more generously for their time and willingness to risk their own health. After all, it is common for workers who engage in other types of risky work to be compensated above normal pay scale. So, I say the industries should compensate their research participants in ways that are commensurate with the risk and inconvenience they are accepting.
Finally, if payment is coercive for research participants, surely it is coercive for researchers as well. Even workers with six-figure salaries can be exploited and manipulated with large sums of money and other favors. Without large payments, doctors and researchers might well be doing the work they are doing, but surely large payments (much larger than any research participant ever gets) must compel them to conduct their research in ways they would not in the absence of such large payments. We might say they have, in effect, had their autonomy stripped from them through coercive payments.
And so it goes.