I applaud them for being so adaptable, many animals can't adapt so easily and have gone extinct.
I also think they are vital to the ecosystem along with rats, flies, and vultures. Imagine all that organic rotting garbage and roadkill we'd have piling up if not for these scavengers! I'd hate to imagine the foul smell from rotting food nothing ate especially with all the garbage cans and dumps nearby my house!
As far as diseases, many animals can carry diseases but that doesn't mean we all get sick, but we treat some species better than others even knowing this. (Our pets carry diseases too!) The #1 disease threat to people are other people...
