Why is it impossible to study social problems with the experimental method?

The experimental method involves controls, specifically for controlling (theoretically) all the factors you consider pertinent to the subject EXCEPT ONE, and then figuring out how varying that factor varies the results. Social problems exist in a realm in which you cannot establish significant controls; by rough definition a social problem is a problem that exists in a society at large...there is no way to establish significant controls on the society at large unless you're God or something.