"This is something courts do fairly frequently to avoid statutory obsolescence and concomitantly to avoid placing the entire burden of updating old statutes on the legislative branch. We should not leave the impression that we are merely the obedient servants of the 88th Congress (1963–1965), carrying out their wishes. We are not. We are taking advantage of what the last half century has taught."
Wrote 7th Circuit Judge Richard Posner, in Hively v. Ivy Tech Community College, which interpreted the 1964 Civil Rights Act to bar discrimination based on sexual orientation (by viewing it as sex discrimination).
Quoted in "The post-constitutional world of Judge Richard Posner," by Antonin Scalia Law School professor David Bernstein. The dispute about statutory interpretation is characterized as a constitutional problem on the theory that a court that gets too creative with its statutory interpretation is acting like a legislature and that ought to count as a violation of separation of powers.