Three-strikes laws are laws that have been passed in many US states, notably California during the last decade of the twentieth century and since, intended to imprison the worst criminal offenders for life.
The essential theme of these laws is that any person who commits a third felony must then be jailed for life without possibility of parole. In the case of felons who were thrice-convicted before the laws were passed, any new conviction would then trigger the penalty.
The underlying philosophy of these laws is that any criminal who commits more than two felonies can justifiably be considered incorrigible and chronically criminal, and that permanent imprisonment is then mandated for the safety of society.
The principal criticism of these laws is that many felonies involve only a minimal threat to society. In some states, possession of a small amount of marijuana may be treated as a felony, so three times carries permanent imprisonment. There are many other felonies which call into question the advisability of strict three-strikes laws, such as some minor white-collar crimes which barely qualify as felonies. Often a burglary, a felony which results in a theft of something of little or no value is perceived as being unjustly included as one of the three strikes.
Another criticism is that these laws provide criminals a perverse incentive to commit murder. If a certain person has two felony convictions, then a conviction for a third non-murder felony (such as grand theft) may carry a penalty equal to that for a murder conviction. If by killing a witness to a crime, the criminal can reduce his chances of being caught, then under a three-strikes law he has no incentive not to commit the murder.