The constition gives SCOTUS the authority to interpret it in cases where there is a dispute. There are several rights that werent in the Constitution but SCOTUS ruled that it was was included. Abortion is probably the best known example. There is also, interstate travel, cohabitation, gay marriage, money being the same as speech (citizens united) and numerous others.
Under the constitution, a SCOTUS ruling is no different than an amendment.
And I've noticed that conservatives really only condemn SCOTUS' when the disagree with a ruling. When SCOTUS rules in a way that conservatives disagree with, they are "tyrants legislating from the bench', but when they agree with a ruling, they have no issues at all.