Why hasn't the human race been wiped out by a killer virus by now?

You would think that someone would have done it by now. Create a virus like the black death but more powerful and spreads more furiously and just kills everyone. With all the war, terrorism and evil in the world you would think that someone would have done it by now. I'm not complaining, I'm so happy that... show more You would think that someone would have done it by now. Create a virus like the black death but more powerful and spreads more furiously and just kills everyone.

With all the war, terrorism and evil in the world you would think that someone would have done it by now.

I'm not complaining, I'm so happy that they haven't but I can't understand why? It makes no sense.
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