The article does specifically mention that the strain used produces an antibody which survives in the gut and may demolish your gut microbiome. Also one of the footnotes mentions that producing alcohol instead of lactic acid as a byproduct may not be as harmless at it seems.

I'm also not sure that taking issue with a company bypassing systemic protections against dangerous drugs is an appeal to authority.

What a strange take! Not an expert (or even a beginner) in this area by any means, but I definitely learned a lot, and I thought the author pretty clearly laid out why they think this probiotic may not be good for your body. Did we read the same blog post?

Did you stop reading halfway through?

Citing published articles is not generally considered appeal to authority.

How does the section titled ‘Category 2: the known health risks of BCS3L-1’ problematically appeal to authority? It seems to about as much as appealing to known results that swallowing vast quantities of lead is a bad idea would. (The other sections certainly appeal to authority, although not obviously fallaciously to me, but that would be to go over quite tired ground about medical regulation.)

The article lists several reasons why the regimen is dangerous: if you get the bacteria that you're supposed to be getting, that bacteria will be continuously producing an antibiotic. Having bacteria constantly dosing you with antibiotics can lead to all the sorts of issues that long-term antibiotics present. Secondly, the article claims, probiotic manufacturing is very susceptible to contamination. Luckily, there are steps a manufacturer can take to avoid contamination, but it doesn't appear that this manufacturer is taking these steps.

All of this is stated in the article, if you missed this on your first read, you might consider re-reading it :)

Many bacteria produce antibiotics to outcompete other bacteria, though, so this isn't new or alarming information. Especially given that, as the author admits, the mutation that causes it to produce that particular antibiotic is naturally occurring in S. mutans!

It'd be a more interesting claim if it was argued that mutacin-1140 was particularly dangerous in the relevant doses (and this somehow never came up in the wild-type S. mutans that produce it).