Pro didn't really address if the garlic "boosts" the immune sytem in fish or not. Thats the reason I will soak food in garlic, to theoretically boost the fishes immune system in order for it to fight off parasite on its own. Not to "cure" the fish because I agree that the garlic won't "kill" crypt.
I'm sure it would be hard to prove if garlic or any other supllements we use like Selcon or Vita-Chem actually boost the immune system or not. Its just like humans taking daily vitamin or Airborne.
I think comparing garlic to palytoxin is a little bit of a stretch. Yes, they are both natural yet completely different. Palytoxin is a "toxin" and garlic is a vegetable. With that said, of course anything can be bad for you or fish if you ingest too much of it. Just my opinions... and I do have much respect for Steven Pro as an aquarist.