how would you feel if someone came and put chemicals on you that made you all 'weird'?
I love that question. Really, I do.
And I can give you a straight up answer on that. See, I don't carry diseases. You don't carry diseases. Most people don't carry diseases. And the ones that do, get theirs treated as best they can. Not too many people volunteer freely for -*test*-('")ing, which is why some companies do their -*test*-('")ing on the rats and mice.
Have a look
here. Ever wonder why nobody thinks twice about killing rats and mice? Especially wild rats and field mice? Well, this site gives a rather comprehensive look at diseases rats carry (AND transmit to humans--see the maroon text). And most likely explains why we don't give a second thought to killing them, and worry when kids decide to have them as pets.