Regardless of which political party benefits from gerrymandering, it should be considering tampering. Gerrymandering is used to manipulate counties one way or another, based on voter preference and/or behavior, which should be represented accurately. By changing the boundaries of the counties, people are creating non-arbitrary boundaries, swaying the political climate of the area. Politics should accurately represent the voters, and gerrymandering undermnes that ideal.
Gaining an advantage through manipulation is hardly ever fair, but it is even less scrupulous when it comes to politics. The act of "gerrymandering" is shameful. Political matters should be decided by the people, not by unknown characters in the background who chop up districts in order to favor one side or the other.
Gerrymandering is unfair because it is designed to manipulate elections rather than allowing a fair and unbiased vote. Politicians redesign districts to ensure a heavy majority for themselves and their political allies, ensuring their party stays in power. Several examples of unfairness in gerrymandering can be found with a quick Google search, there are even games to play that expose one to the evils of gerrymandering.
A person's vote should count. A person's vote shouldn't be moved to a specific group so that it will be less influential. Districts should be fashioned in a way that makes geographic sense. Then, a politician should live with it, whether they win or lose. Ultimately this is more fair than trying to decide regions so that they will vote a certain way.