Eating an animal that died of disease might be deadly for a human.
Scavengers have ways to fight the deadly bacterium and some diseases.
And even they can die from some diseases.
now closer to the topic:
That's true I can kill a bug while I'm walking and I definitely kill harmful bacterium that is attacking my body or would have attacked it if my immune system wouldn't have killed it.
Sometime killing is necessary sometime it's accidental.
The question might be: Is killing animals that suffer the way we suffer a necessary thing?
And many plants aren't killed when fruits are harvested, so eat fruits Bros and Sis the most ethical and healthy food. The Food of Gods.