What does Ignorance Kills mean?

It means people do dangerous things because they don't know any better. A convert saying might be, "Education saves lives" or "Information saves lives."

(And, by the way, "ignorance" just means you have no knowledge of something; it does not mean "stupidity")

It means that being unaware of something, being poorly informed, could harm or even kill you.

A simple example would be knowing that you shouldn't purchase or eat the contents of a can that has a bulge or swelling in it. The bulge could signal botulism poisoning, which can be fatal.

This is the opposite of "ignorance is bliss." I don't hear it very often, but I interpret it as ignorance being a fatal limitation. In other words, ignorance diminishes the ignorant.

You being stupid, dumb, without conscience, can kill you or (most likely) bring you to kill others.

Like when you have an ideology that leads you to believe strongly that Whites are more deserving of life and love than Blacks. That can easily lead you to kill Blacks.

Edit: Dumbness is the friend of ignorance.