Appeal to novelty

Appeal to novelty is the fallacy of believing that something is good or true because it is new.

Examples

 * "A new version of the server software just came out. We should upgrade to it, because it's the latest version."
 * "Homosexuals have been repressed for centuries, as have atheists. But in recent decades, gays have started publicly announcing themselves as such. We atheists should do the same."

Counterarguments
While many new ideas are good (after all, every good idea was once a new idea), novelty on its own is no guarantee of quality. Many new ideas are bad as well.

Lack of testing
A new idea or product may have flaws that have not become apparent because there hasn't been time to find them, or because not enough time has passed for the flaws to manifest themselves. For instance, a new drug may have side effects that only become apparent after decades of use. New versions of software packages often have flaws that the testers did not foresee, and which become apparent only after the software has been tried in many different environments.