Your understanding is flawed in this case. The Constitution doesn't say everyone has to drink from the same water fountains or attend the same schools either, but state-passed laws saying that water fountains and schools are only for certain races is unconstitutional nonetheless. Which was determined FIRST by courts, and only later by legislation.The constitution never states marriage. Its my understanding that they are interpreting the word happiness to include gay marriage and IMO that is very much a stretch and how I feel about the issue shouldn't come into play. A referendum was the thing to do.
Something doesn't have to be specifically delineated in the Constitution for a Constitutional violation to occur when a law is passed on that topic. I'm sure the Constitution does not specifically say anything about how it's not okay to murder Texans in California, but a law saying it is okay to do so in California would be unconstitutional, and stricken down by the courts. And that would be the judicial system working perfectly - though some would call it legislating from the bench.
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