Comment by zenexer
Because the participants could very easily spread it to other people. This wouldn’t just affect them. That’s why the trial was ultimately required to take place under quarantine.
It’s not even a question of whether it would spread, but whether it might spread. There’s a reasonable chance that this bacterium would, in fact, spread, and nobody has proven otherwise.
The FDA is doing its job here: it’s protecting the masses from people who believe they’re just consenting for themselves.
The FDA, however, is not regulating the spread of the 800 other known species of oral bacteria as well as presumably numerous unknown ones, which do cause some known harm. The extreme suspicion of commercially introduced anthropogenic agents seems a bit ridiculous in both natural ecology and the human microbiome. Prove this compound conclusively safe, but not these other ten million compounds we're just going to allow to run wild. Or for competitors - rely on the 'proof' of safety established in the 1920's or the 1970's before we had any idea whatsoever what we were doing scientifically. Or just rely on doctors/dentists unsupported first-principles advice - we've never demonstrated scientifically that floss works, for example.
We should all be quarantined, all the time, by this criteria. Regulatory bodies have a great cognitive bias towards fictional 'purity' of systems that are in actual scientific fact, messy and routinely contaminated in various ways.