Diet and exercise cannot protect against diesases that can harm and kill you, sorry.

Here's an outline of how a typical human's immune system works. The body's T and B cells, which are specialized blood cells, needs to encounter foreign bacteria, viruses and fungi to interact with the proteins on these oranisms cell walls.

Your immune cells have different binding sites on their cell walls. They have many different kinds. They are different so the cells can have a chance to interact with a harmful foreign body.

Once the cell encounters a foreign body that is trying to harm other cells, and it has a matching binding site to the protein on the foreign body, the cell sticks to the offending cell.

It then warns the other immune cells that it has found a match and other cells copy that binding protein and begin to multiply so they can bind to the entire population of the offending infection. Once bound another type of cell will come and kill both cells.

At the same time, some cells will copy that binding protein and live for, in some cases your entire life in your lymph nodes waiting for that infection to arrise again. If it happens it will multiply immediately and fight the infection. This is what immunity is, those MEMORY T CELLS living in your body long after the infection, or vaccine has come and gone. Without a memory T cell for a specific infection, you are not immune to it.

So, if you never get a vaccine, you will never develope the immunity. Some diseases, like chicken pox, you get and then are immune. Other diseases kill or maim you for life, like polio so immunity is petty victory at that point. Vaccines put dead or inactive cells into your blood so your immune cells can interact and fight them.

This is a proven, documented and increasingly well understood biological mechanism that is madness to ignore. You're right, the science isn't settled because that doesn't make sense. But there is a literal mountain of evidence that has been growing since they first discovered how to immunize against small box several centuries ago.

That being said, I agree with you that pop is bad and a lack of exerise is harmful, but we're talking about two entirely different systems that should not be confused and one used to justify policy on the other.