The Tuskegee Study wouldn't have happened if its participants were voluntarily, and it's effects still haunt the scientific community today. The attitude of "science by any means, including by harming other people" is reprehensible and has lasting consequences for the entire scientific community.
However, unlike the Tuskegee Study, it's totally possible to have done this ethically by contacting the leadership of the Linux project and having them announce to maintainers that anonymous researchers may experiment with the contribution process, and allowing them to opt out if they do not consent, and to ensure that harmful commits never reach stable from these researchers.
The researchers chose to instead lie to the Linux project and introduce vulnerabilities to stable trees, and this is why their research is particularly deplorable - their ethical transgressions and possibly lies made to their IRB were not done out of any necessity for empirical integrity, but rather seemingly out of convenience or recklessness.
And now the next group of researchers will have a harder time as they may be banned and every maintainer now more closely monitors academics investigating open source security :)