Chelation therapy is a specific treatment for specific kinds of heavy metal poisoning. It only works at all when caught early enough that the substance hasn't been absorbed into the body's cells.
As an example, arsenic poisoning can be treated with very specific sulfur-containing medicines.
Certain chemical processes can increase the body's ability to absorb the toxin, which may make it impossible to remove it from your body. Chelation can only remove specifically targeted compounds from the bloodstream.
Another example, hydrocarbon-containing mercury compounds found in some beauty products. Mercury does not absorb through the skin in its elemental form (acute mercury poisoning from this is due to inhaled vapours coming off the liquid metal). "Methylated" mercury absorbs extremely well through the skin, and eventually the blood-brain barrier, leading to all sorts of irreversible (and often fatal) neurological damage. This is because these compounds are lipophilic, they want to mix with fats and are not water soluble. Hydrophilic substances are cleaned from the blood by your kidneys, and secreted as urine. Your brain is mostly fat and tends to accumulate these compounds.
There's no such thing as "bad" bacteria, unless you mean ALL bacteria. Perforate your colon if you want to find out how bad your gut biome is for the rest of your body.
When hydrogen bonds with other elements, it typically creates acids. Your body is normally really good at maintaining pH, but if you think drinking bleach is a good idea your body is not functioning normally.
One last comment about chelation, that medication is administered via IV in a carefully controlled environment for a reason. If 3 little spritzes under your tongue was going to have anywhere near the same therapeutic effect, it would have to be absurdly concentrated (to the point it'd be toxic on its own). Chelation, generally, works by binding to and "trapping" the toxin. This makes it soluble in water, which your kidneys concentrate in the urine, so you can safely pee it out. You need a fairly large dose over a long period of time to have the best outcome. If you have kidney or liver problems, it might not do anything at all.
The rest would take too long to explain. Symptoms have so many overlapping causes that you really do need to talk to a doctor if you're having issues (especially those that MMS claims to "treat"). It's not gatekeeping, technically anyone can learn about differential diagnoses/drug interactions/et al, it's just A LOT of information.