Follower of the idea of Utilitarianism (by escherIV). In this philosophy, morality is based on the consequences of a person's actions. A morally good action is that which most benefits society, or moves us closer to utopia. A bad action is that which makes people unhappy without any perceivable benefits to society.
Thus, a utilitarian would say that putting a murderer in jail, or executing him, is morally justifiable because society benefits from having fewer people randomly killed. Placing someone found in posession of a substance like marajuana in jail is NOT morally justifiable because it makes that person unhappy and doesn't do anyone else any good either.
More genrally, we feel that any action that does no harm to others should be allowed. Good and bad are things that must be decided upon based on some sort of analysis. Just because somebody thought at one time it was wrong to have a divorce (NB by dizzy), doesn't mean that we should never have divorces anymore.
Morality is relative to the society in which an action occurs. For example, at one time, many societies may have found advantages to having large populations. It makes sense for such a society to decide that homosexuality is bad since it slows population growth. If, however, the society's population increases to such a degree that the resources of the globe are ruthlessly destroyed in supporting that society, it may make more sense to think of homosexuality as good.