What baffles me is that the people who are doing these things are too blind and illiterate to understand basic conceptions.

What if someone is in the country illegally and has an infectious disease like tuberculosis and they don't go to the ER because they are afraid someone will report them?
(For those who are not aware Tuberculosis has not been eradicated in third world countries and is HIGHLY infectious.) If they're not treated, they could spread it to anyone they're in contact with. The person could spread it to his/her spouse, kids, coworkers, etc.