I mean, he's not presenting the evidence here in a hacker news comment, but that doesn't mean the evidence doesn't exist. There are a bunch of different categories of stabilizers, and only some of them have antimicrobial properties -- most are about maintaining moisture and loaf volume over time.

There are three substances that are predominantly used to inhibit mold growth, though: calcium propionate, potassium sorbate, and sodium benzoate.

The first two are extremely well understood and considered safe globally. The third is still considered safe, but might have some interactions with vitamin C that lead to benzene formation to the tune of several parts per billion. The FDA considers this safe, and has for some time.