Colloidal Silver is far less injurious and for that reason, the FDA should leave it be. However, they will not and they will not leave zappers alone either.
The problem is that both work and that is a threat to the medical 'status quo' and their profits.
I had this well explained to me by 2 different 'former FDA prosecutors' when I was looking for a good attorney.
We ended up using Ralph Fucetola, The Vitamin Lawyer, who is very pro Colloidal Silver , supports zappers, and also Jonathan Emord who has defeated the FDA on many occasions.