Science and scientific studies help determine what is ineffective or harmful, the problem is the FDA doesn’t have authority over shit plenty of things - a person can go on YouTube and say drinking their special bottled water will cure cancer, and they don’t fall into FDA guidelines so they are free to claim whatever they want, essentially. These woo-woo type cure-alls have gotten into trouble with the FDA because of their ridiculous and unfactual, unproven claims, but that’s usually where the lawyer wordsmiths show up to change the wording just enough to not get into trouble with the FDA.

There is a whole history of pseudoscience as an industry and how it was able to bribe/lobby for its current position in public view (since you even have to ask this question)