As society’s ideas of what is unacceptable behavior changes, crimes also change over time. Things that were once crimes (like adultery) are no longer…

As society’s ideas of what is unacceptable behavior changes, crimes also change over time. Things that were once crimes (like adultery) are no longer criminal. Others have become crimes only recently (heroin was legal as recently as 1925). Some crimes still on the books are no longer actively enforced, such as cattle-rustling.
This is desirable; as society changes its perceptions about not only what’s right and wrong, but how serious a violation is, laws should change as well. It suggests that the criminal laws change in response to society’s views. This is in contrast to civil laws, where often the law precedes the attitude adjustment of the society (Brown v. Bd. of Education, for example) and even when it’s been made clear, society and its governing bodies often drag their feet (Brown I, the first time the case came up at the U.S. Supreme Court, was originally decided in 1954. The 10th U. S. Circuit Court of Appeals noted in Brown v. Bd. of Education III that vestiges of segregation persisted in Topeka schools in 1989, 35 years after was originally decided).