Food produced by Fritz Haber's Haber-Bosch process (making fertilizer) supports about half of the world's population.
Phil Spector produced music which meant a lot to a lot of people. Still a murderer.
Harold Shipman Saved the lives of thousands, yet should always be labelled a mass murderer because he knowingly positioned hundreds.
Probably not though, I don't think a typical GP saves thousands of lives
It really was a two-man team that discovered nitrogen fixation - the other being not Carl Bosch, but Robert Le Rossignol who assisted Haber in developing his bench-scale nitrogen fixing reactor. Carl Bosch led the team that scaled it up, and that was a large effort of hundreds of people.
The Haber–Bosch process was never a two‑man mission to “feed the world.” Haber devised a laboratory method to fix nitrogen, and Bosch led the first industrial‑scale implementation, but neither of them was personally producing, optimizing, transporting, and applying fertilizer across the globe. Turning that reaction into most of the world’s nitrogen fertilizer required teams of chemists, engineers, metalworkers, factory operators, agronomists, logistics workers, and farmers, and an entire century of industrial expansion. If it truly were a two‑person accomplishment, we would only need a handful of farmers per country, which is obviously not how agriculture or industry work.
That is literally true, but for anyone who hasn't studied plant biology, I think that "some plants have evolved specific structures to host obligate symbiotic bacteria that obtain nitrogen from the air and convert it into a form usable by the plant" is close enough to "many plants can obtain [nitrogen] from the air".
(A link for anyone not familiar with this: https://en.wikipedia.org/wiki/Root_nodule)