Prop 8 was of the people, as are all the constitutional amendments passed in many states explicitly defining what marriage is or isn't. Isn't that independence of the people? Who is it that's against independence now?
The 14th Amendment reads in part, "All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws."
Note that the only two descriptors of people are "persons" and "citizens." It doesn't talk about white, black, native, asian, gay, straight, or anything else. The only thing that counts is "citizen." So even if your state passed an amendment to its constitution that said black people couldn't drive on Sunday, it would be unconstitutional. This is the same reason the court invalidated laws prohibiting inter-racial marriages in Loving v. Virginia in 1968, a point which seems to have been lost on Justice Thomas.