airborne viruses that can travel for hundreds, perhaps even thousands of miles

Airborne viruses usually travel about two metres (hence the two metre social distancing rules for Covid-19). Even if a single virus somehow travels farther - perhaps by hitching a ride on a vehicle - it is unlikely to cause a successful infection, because you need enough of them ('viral load') to overwhelm host defences.

I don't know what 'diluted toxins' has to do with viruses and immunology since toxins are a rather different matter entirely

Vaccines work in different ways. The oldest method is what you described - attenuated viruses. Newer ones usually do not contain active viruses. They either have inactivated viruses, or, increasingly, just the viral proteins or mRNA. This reduces the risk of the vaccine causing harm to the recipient.

the immune system can 'learn' and 'evolve' over the course of a single human's lifetime

If the person survives, their immune system may learn to identify and defend against that virus. Or it might just forget. Or it might cause random damage due to cytokine storms. Or it might forget all previous information. And in any case, some percentage of the population will die.

Thinking that infections are good because they will help increase immunity is like thinking that a country constantly being at war is good because then they'll always be ready for war. Particularly when you can give the same immunity at a fraction of the risk using vaccines that just have some proteins or mRNA.