First responders, firefighters, and soldiers are allowed to volunteer for hazardous missions. Why should people, (soldiers or civilians) not be allowed to sign up for comparably hazardous medical experiments that are judged by a special government committee or whatever to save a large number of lives in total/net?
In discussions of this question by professional bodies and elsewhere, there seems to be a consensus that volunteers, even when fully informed and fully and freely consenting, must not be exposed to a risk of death or injury or the same magnitude that a soldier could ethically be.
"An ethics panel denied the application in January 2017, saying that deliberately infecting volunteers with Zika — which is innocuous to most people but can profoundly damage the brains of fetuses infected in the womb — would pose too much risk to the participants and their sexual partners." Source: https://www.statnews.com/2020/05/01/infect-volunteers-with-covid-19-in-the-name-of-research-a-proposal-lays-bare-a-minefield-of-issues/
Here is a link to a readable non-paywall-protected scientific peer-reviewed paper by Ricardo Palacios about this: https://trialsjournal.biomedcentral.com/articles/10.1186/s13063-019-3843-0 . I haven't seen an explanation or justification for this position that seems to be the consensus at the moment.
Doctors and nurses have worked in conditions where they were in grave danger of contracting covid-19/SARS/whatever you want to call it. No one protested that this was not ethical, provided a lot of lives were saved on balance, not even when some of said doctors and nurses died of covid-19 contracted as a result.
For example, if a minimum of one hundred people to a maximum of ten thousand people would be saved from death by covid-19/SARS/whatever you want to call it, for every death of a volunteer in an experiment of a particular type, would that be ethical?
Please don't explain how or why the public have a particular set of feelings about this sort of experiment. This question is asking whether it is actually ethical and why or why not.