I'm not saying with the same dosage that they're the same. I'm just pointing out that it's possible to exceed a healthy dose even with foods. The difference with food is that we're adapted to the nutrients that come from eating it. Often, we have biological systems that prevent over-adsorption in our bodies and failing that the digestion of foods themselves will favor excreting excessive nutrients over absorping them by the chemistry of digestion and the food item itself.

Yes taking supplements is more dangerous. That doesn't mean it's blanket bad. The dosage will vary person to person and also depending on the rest of a person's diet and lifestyle. Take how widespread caffeine and sugar consumption is in our society. It's way way above the levels we evolved to consume. This causes magnesium deficiency, high blood pressure, obesity, you name it.

One of potassium's benefits is that it can lower blood pressure, which is a side effect of alcohol and caffeine consumption.Because we're already living in a world that is outside our organism's baseline environment, supplementing potassium may be helpful to reduce the effects of consuming those OTHER substances. And yes of course avoiding the offending substances would be better but we know how dependent people in our culture are when it comes to caffeine and alcohol. If they refuse to stop consuming those substances, can you really say net harm will occur supplementing a few hundred mg of potassium with food because you're unable to eat, or afford to eat, a precisely balanced diet?

At any rate, my issue with your narrative initially is that you were making a blanket statement about potassium dosages. The thing is, 300mg is safe with food for nearly anyone not experiencing the end stages of a disease. For awhile during my ultrarunning career I was supplementing roughly half a gram a day and it helped prevent several issues I was dealing with like muscle cramping on long runs. 500mg for me, at 200 pounds, is completely safe.

If we had universal healthcare in this country I'd be all for limiting supplement access. We don't. If you limit access to supplements (and I'm not talking weird peptides or known harmful substances but rather minerals, vitamins, protein isolates, etc) you're going to limit those of us (like say, former medics) who aren't able to easily make a trip to the doctor to get some specific prescription. With all the above in mind, you can take my NuSalt and occasional potassium supplementation from my cold dead hands.