You do realize how viruses work right? and how your body fights them right?
For small pox:
Of all those infected, 20–60%—and over 80% of infected children—died from the disease
You do realize how freaking scary that is right? Sure it's not a 100% death rate, but 80% in children is damn close, and 20-60% in adults is really damn scary.
Just think, at a 50% death rate, you would need each living person to bury another living person. Sure Evolution "somehow" favored our ancestors, but that doesn't mean any of us are immune to it by any means.
There is a reason why the ENTIRE world worked together to completely eradicate small pox from the face of the planet. The first (and only to my knowledge) time the Human Race as a whole set out to completely destroy another species from our little rock in the universe.
If your not vaccinated and your not scared of smallpox, then you need to pick something you are scared of go look up it's death rate then compare it to smallpox, maybe then you will have an understanding of the magnitude.