Critics of the Marshall Protocol tend to attack it on four bases--
1. Vitamin D
2. double-blind studies
3. esoteric scientific theories about why it can't work
4. ad hominem attacks against Dr. Marshall
--according to what I have found online so far. I will try to address these criticisms one by one in the coming days. I am working this out for myself so there's no telling where this will take me.
I do find it interesting though that I haven't found any criticisms of the drug protocol itself, even though the usage of several of them is "off-label." There is just the general suggestion that taking antibiotics long-term (for two years or so) must be inherently bad.