There's no question that quarantines prevent the spread of disease: there is plenty of question as to whether the disease justifies it; including in the cases of SARS and MERS.

For example: most new flus come out of China due to their agricultural practices; building a wall around China until they change the practices and isolating people in the rest of the world population who get it would actually remove the flu from the human experience. I believe flu killed 60,000 people in America last year. Are we ready to do that? Should only take a couple of years!