The FDA Office of Criminal Investigations, the direct enforcement branch of the FDA, uses bonded LEOs to do the enforcement under their perview. While the majority of actions go through civil proceedings (lawsuits), any investigatory work for those lawsuits is done under the direction of the FDA's federal law enforcement officers (or their contracted representatives). That's how enforcement works in the US. If you want to avoid that, it would require a complete restructuring of the entire US legal system from the ground up.
And there is harm when people take misinformed medical advice from people claiming to know better.
Yes, but that harm is resolved in civil court unless the person in question is criminally liable, usually through gross negligence because they have something like a duty of care. The Alex Jones case, which you brought up as an example, is not in any way comparable to that.
(edit: for clarity, bonded LEOs are what you think of as a cop, instead of someone like a building inspector who is technically law enforcement but does not have the ability to do things like make an arrest or charge criminal proceedings.)