In a functionalist society, do people need to agree within the society, or is it that they perform the actions in order to conform?

In my opinion, the functionalist perspective in sociology
tells us nothing about why individual people act in the ways that they do. 
Functionalism is about the society as a whole, not about the
individuals.

So, for example, functionalist theory says
that crime and deviance exist because they help to define who we are.  We define who we
are by saying who we are not -- by saying "those kinds of behaviors are criminal or
deviant; they are not acceptable to us."

But this does not
say anything about why the individual criminal commits a crime.  It only speaks about
why crime is "important" to our society.