We tried that approach for millenia but sadly young people with poorly developed immune systems and old or sick people with compromised immune systems kept dyin

We tried that approach for millenia but sadly young people with poorly developed immune systems and old or sick people with compromised immune systems kept dying and we decided as a society to do something about it because some of us have kids and parents we love. Then a bunch of selfish ignorant hippies decided, based on their limited experience of living in a society protected by vaccination, that disease was a problem for poor foreign people and they didn't need it. While an outbreak might kill off the DNA of these people and their offspring and improve the gene pool it might also do some collateral damage. There are some legitimate reasons people have not been vaccinated and as vaccination simply strengthens the immune response it is more effective for some people than others. You would hate to run into a coughing wheezing infected family of alternative medicine believers on the week you took a shot depressing your immune system to fight your crippling auto-immune disease or protect your transplanted organ from rejection regardless of your vaccination status.