Supreme Court Injustice

In the U.S., our supreme court is not elected by the people. There are only 9 of them (usually), and they serve as long as they want, even until they die. Their influence on our lives is immense, and lasting, as their decisions also set precedence for future decisions. In addition, our judicial branch is set up in a way that encourages our judges to uphold earlier decisions rather than evenly consider both new and old opinions on an issue. The combination of these factors creates a potentially very corrupt and stagnant system, although the members are often extremely intelligent and respected, there's no guarantee that they will perform well.
Our nation has grown considerably since the number 9 was selected for the supreme court, so allowing a larger number of people to serve in this court would likely increase the diversity of opinions and encourage more effective deliberation. It's not rational to allow only 9 people to represent the supreme court of our nation of over 300 million people. The fact that they do not serve limited terms, means that a lot of them probably have very dated views. It would be absurd for U.S. citizens to expect a person, from a far away generation, to accurately and actively change their opinions with time, to reflect the progression in thinking that we acquire. This system is rooted in slowing down progress, likely out of fear. A result of this is that only recently is a thing like gay marriage being regarded as a right, as it should have been a long time ago. It's hard to imagine any true justification for having denied this right, yet when you look at the people in power in the supreme court over the previous years, it's hard to figure out what their incentive would have been for allowing it. This supports the idea that the court should have more people who represent more varied views.