Appeal to tradition

Appeal to tradition is the fallacy that something is good or correct because it is old.

Examples

 * Many people attend the church their parents attended, perhaps carrying through several generations, and when asked to defend their beliefs use the fact that it is a family tradition to argue its validity. "I believe it because my parents believed it."
 * Those opposed to gay marriage often argue that since marriage was originally a bond between a man and a woman exclusively, it should now be defined in law to require a similar heterosexual relationship.
 * Some people believe the United States electoral system should be changed to reflect current social standards, while others (making an appeal to tradition) say it should be kept as-is. "It has worked for over 200 years, so we shouldn't change it."

Counterarguments
The mere fact that something is old does not mean that it is good: throughout most of human history, people have kept slaves, but slavery is now universally recognized as being evil. On the other hand, people have lived in houses for thousands of years as well, but that does not mean that we should stop building houses: old ideas can be good as well.

Changing conditions
Sometimes, conditions change so that the reasons that originally supported an idea no longer hold. For instance, in the 17th century when the US constitution was ratified, travel was difficult and news traveled slowly, so it made sense for voters to elect a representative who would travel to the capital, learn about the presidential candidates, and vote on behalf of the people in his state. With the advent of mass media, however, individual voters can easily learn about the candidates, so this particular justification for the electoral college no longer holds.