Explain the concept of 'original intent' in the Judicial Philosophy of the US Supreme Court

As set out in Article III the judicial branch's role is to protect the constitution and the rights and civil liberties of the people; in doing so judges are granted the right to interpret the constitution (judicial review) relating to actions and cases brought to them; as established in the case Marbury vs Madison. 'Original intent' is one way to interpret the constitution, often adopted by conservative judges, who consider the original intentions of the founding fathers and the conditions of their society when analysing the constitution and making decisions.
Showing restraint rather than activism in decision making is often a result of originalist philosophy; as many judges believe it wasn't the Framer's intention for the judicial branch to make any drastic changes to the constitution but the Legislative branch's prerogative to amend it. For example, in 'Texas vs Johnson' judges didn't necessarily agree with the burning of the American flag, Johnson's freedom of speech was upheld in tradition with the first amendment. However, originalists do face criticism from more progressive / constructivist thinkers who argue the constitution is a 'living document'. For instance much of the civil rights movement would have been stifled if it weren't for judicial activism and moving away from original intent; as demonstrated in the historic ruling of Brown vs Topeka which brought the legality of segregation in America into question for the first time.