So let's vastly improve the estimates of lifetime cancer risks by giving volunteers high doses of suspected carcinogens.
Science has done things much worse than that. Heck, in the 60's researchers in New York infected retarded children with hepatitis just to investigate gamma globulin.
There are an amazing number of advances we could make if the medical ethics people would just allow us to implant experiments inside human brains, conduct live brain tissue sampling to see what genes are turned on, separate twins to raise them in controlled environments to get a better idea of nature versus nurture, and closely track or control the development of human embryos to see which genes are getting switched on, and why. Heck, imagine the advances we could make in understanding human sexuality if we could just try altering the brains of homosexuals, or fetuses, in a carefully controlled study the tries a host of different hormones, genes, and growth factors.
Scientists sometimes step over the line, and sometimes where they step is what makes us realize that there should have been a line when one didn't already exist. The groundbreaking Nazi experiments are why the world adopted rules of medical research ethics and gave them the force of law. Scientists who are convinced they are saving humanity are among the worst offenders, because saving humanity can justify just about anything. Heck, a recent climate change paper was yanked because it grossly violated the standards and ethics of numerous psychological organizations. Those standards were of course put in place because of previous unethical studies.