Potassium iodide is not iodine; it is a compound of iodine, with the same relation to iodine that table salt (sodium chloride) has to chlorine gas, which is a chemical weapon. In fact, both potassium iodide and sodium chloride are alkali halides, compounds of the halogens iodine and chlorine, respectively. Iodine is extremely reactive and consequently toxic, not only to people, but even more so to bacteria, which is why it is useful in disinfecting water. Tincture of iodine typically contains both potassium iodide and elemental iodine, but it's the elemental iodine that does the work.

Iodine, on contact with electron donors, will rapidly reduce them and ionize to the same nontoxic iodide found in potassium iodide, rendering it nearly harmless. However, oxidizing your body cells causes chemical burns by killing them; oxidizing bacteria and fungi kills their cells too. Pure iodine will blister your skin on contact.

Essentially your optimism arises from confusing two related, but very different, substances. Don't feel bad; I've made similar errors any number of times. One out of every ten thousand times that you think you've found an easy way to hack around a difficult and important problem, it's a breakthrough. The other 9,999 times, you're overlooking a fundamental reason your idea won't work.

It's deeply unfortunate that HN is not the kind of place that people will correct your mistakes, as I've done above, instead of silently downvoting you.

If you are using CNS stimulants (amphetamines, methylphenidate, modafinil, cocaine, maybe even caffeine) you might want to cut down your dosage. The hyperfocus they facilitate can be counterproductive when it causes you to overlook your errors and get overexcited over a possible breakthrough. This can blossom into full-blown amphetamine psychosis, which is not an experience I recommend, especially for the people around you.

A useful tool in discovering errors like this is investigating consequences that would ensue should your reasoning turn out to be true. For example:

* Potassium iodide is a chemical that people have been dosed with many times, including soldiers under controlled conditions. If it cured everything from jock itch to acute bacterial meningitis, probably someone would have noticed.

* Bottles of iodine are labeled "for external use only". If it were nontoxic, it would not be labeled in this way.

* Many potassium iodide vendors and customers are enthusiastic promoters of colloidal silver, which actually is a broad-spectrum antimicrobial that is fairly nontoxic to human bodies. (By itself, it's not effective enough to disinfect water with, but in combination with the more toxic copper, ionized silver has been used to disinfect water.) If KI were effective for disinfection, they would be promoting it as such.

* Our bodies use iodide in certain thyroid hormones, so there are enzymes devoted to moving iodide ions around, keeping them from reacting with the wrong things, etc. This is different from e.g. lead, mercury, or tellurium, which have no known biological function and cause toxicity by acting as poor substitutes for other atoms. If iodide were nontoxic and effective at stopping fungal infections, we would have evolved to concentrate it in our bodies and direct it to areas suffering from inflammation. But we didn't.