Although once considered a leading theory of deviance, strain theory has come under criticism for its narrow focus on poverty as the primary cause of deviant behavior. Recent efforts have sought to revise and extend the basic principles of the theory by expanding and reformulating ideas about strain. Robert Agnew (1992) has made the most notable revisions to the theory. His reformulation emphasizes social psychological, rather than structural, sources of strain. Agnew also broadens the concept of strain, arguing that poverty may be a source of strain, but it is not the only source. Three sources of strain are important: failure to achieve positively valued goals, removal of positively valued stimuli, and confrontation with negative stimuli. The first type of strain, failure to achieve positively valued goals, may be the result of a failure to live up to one's expectations or aspirations. Strain may also result if an individual feels that he or she is not being treated in a fair or just manner. The removal of a positively valued stimulus, such as the death of a family member or the loss of a boyfriend or girlfriend, can also result in strain. Finally, strain can also be produced by the presentation of negative stimuli, such as unpleasant school experiences. Thus, although this reformulation of strain theory retains the notion that deviance is often the result of strain, the concept of strain is broadened to include multiple sources of strain.
As you can already tell, Functionalism is more positive and optimistic than Conflict Theory (the basis for much criticism by many Conflict Theorists). Functionalists realize that just like the body, societies get "sick" or dysfunction. By studying society’s parts and processes, Functionalists can better understand how society remains stable or adjusts to destabilizing forces when unwanted change is threatened. According to this theory most societies find that healthy balance and maintain it (unless they don’t and collapse as many have in the history of the world). Equilibrium is the state of balance maintained by social processes that help society adjust and compensate for forces that might tilt it onto a path of destruction.