Judge Stephen Reinhardt wrote for a unanimous three-judge panel that laws that treat people differently based on sexual orientation are unconstitutional unless there is a compelling government interest. He wrote that neither Idaho nor Nevada offered any legitimate reasons to discriminate against gay couples.
Homosexuality is fundamentally at odds with the proper ordering of things. In the case of males, sanctioning homosexual marriage sends the completely incorrect signal too youth that penises belong up male rectums, which they clearly do not. Such homosexual activity is fraught with all sorts of negative physical and mental consequences. It promotes extreme sexual-risk-taking including sex by, and with, HIV/AIDS infected persons and rampant promiscuity, which occurs at high rates in homosexual "open" marriages where monogamy doesn't demand exclusivity and faithfulness but rather allows spouses to still sleep around or to engage in orgies, etc. Lesbians do not escape serious negative impacts either.
In addition, the exact arguments used by the court to allow same-sex marriage apply to polygamous unions, incestuous unions (we've seen the German's ethics council arguing for incestuous marriages along these exact lines), and, frankly, all manner of sexual anarchy leading to the utter degradation of society and civilization.
If working to prevent all that via laws forbidding homosexuality, with its inherent problems, is not a compelling state interest, nothing is.
The ruling opens Pandora's Box. The judges are very shortsighted.
There was nothing wrong with the absolute prohibition against homosexuality. It was a good thing. The dark side has undermined it and is working to undermined the whole of humanity. Other nations will be well-advised to avoid following the increasingly decadent USA.