[iamthirsty]

There no intent to personally harm with a disease/virus — it's just what they do and one of the players in the game of life.

Versus someone calling you specifically to cause harm, especially when they can comprehend the harm they are intending to inflict, in your example.

[Nasrudith]

Predators also 'play the game of life' and humanity is downright vindictive about any who prey upon them. I personally suspect the real difference is how incredibly hard it is to target a disease. Hell, just identification of what a disease really is was spotty for millennia.