While you may have gotten Rubella, and chicken pox as a child, and had no complications, some did. However, getting around a pregnant woman, before realizing you had either, and exposing them to it, could do a lot of damage, and even kill the unborn child. I'll admit that Rubella, measles, and chicken pox are not necessarily the worst of the lot, but anti-vaxers are also against Diphtheria, Polio, Typhus (typhoid fever) Small Pox, and Tetanus vaccines as well. Read up on how horrible the pain, and suffering from some of those diseases can be. Tetanus causing Lockjaw is especially horrid.
Again, the numbers of reported mortalities, prior to the vaccines, are available. The numbers are staggering. Considering too, that they were not as meticulous with record keeping, and some of the deaths from these diseases went unreported, the actual figures were somewhat higher.