Liberal or Conservative minds in the Supreme Court, does it matter?

It really does matter if a Supreme Court Justice is conservative or liberal. The Supreme Court justices aren't suppose to be influenced by their own views. They are supposed to strictly interpret the constitution. However, they are human, and their own values tend to influence their decisions. This is why it matters so much if they are conservative or liberal. What if Congress and the President pass a law that gay people could marry? If someone challenged this law all the way to the Supreme Court, they would have to decide if it was constitutional or not. If the Supreme Court justices are mostly conservative they could vote that it was unconstitutional. Their job is to give a voice to the Constitution, not use their own to make decisions that they want to see happen. What if one of the laws said that people who were taller than 6 feet got a tax cut and all of the Justices were taller than that. They could use their power to say it was constitutional because it benefits them. How can we make sure their making their decision based on the constitutions and not their own views? How can we make sure that the Supreme Court justices don't use THEIR views to make their decisions just the constitution's? How is that fair for the people? Do they have too much power?