To argue this, there are two major points that should be made.
First, those who believe in judicial restraint often claim that justices should stick to the “original intent” of the Constitution. Advocates of judicial activism say that this is not possible or desirable. It is not possible because we cannot know exactly what the Constitution meant in a given case. The Framers could not have, for example, imagined GPS devices being used to track cars and cannot have had an “intent” on that issue. Furthermore, there is no reason that we should be bound by the social values of people from 225 years ago.
Second, we can argue that the judicial branch should be fully equal to the other branches. There is no reason, in this view, for the judicial branch to defer to the elected branches. The judicial branch has just as important of a role to play in our constitutional system of separation of powers and checks and balances. Therefore, it must engage in what some would call judicial activism.