More likely this had to do with verification of signatures and fraud, but then, I'm a cynic.
The Supreme Court decided 8-1 that the signatures must be made public. Only Justice Thomas, which seems ironic, supported the metaphorical hood of secrecy over hatred.
It's important to note that this is not a complete victory for this case. What they do is send the case back down for consideration. They found that generally things should be public, but several justices seemed to say that there might be times where secrecy could be justified.
Not Justice Scalia, though. I'll hand it to him, he's for transparency all the way:
Plaintiffs raise concerns that the disclosure of petition signatures may lead to threats and intimidation. Of course nothing prevents the people of Washington from keeping petition signatures secret to avoid that—just as nothing prevented the States from moving to the secret ballot. But there is no constitutional basis for this Court to impose that course upon the States—or to insist (as today’s opinion does) that it can only be avoided by the demonstration of a “sufficiently important governmental interest,” ....And it may even be a bad idea to keep petition signatures secret. There are laws against threats and intimidation; and harsh criticism, short of unlawful action, is a price our people have traditionally been willing to pay for self-governance. Requiring people to stand up in public for their political acts fosters civic courage, without which democracy is doomed. For my part, I do not look forward to a society which, thanks to the Supreme Court, campaigns anonymously (McIntyre) and even exercises the direct democracy of initiative and referendum hidden from public scrutiny and protected from the accountability of criticism. This does not resemble the Home of the Brave.
The real question will be whether everyone who signed that petition, (a) really signed it, or (b) knew what they were signing. During the campaign there were numerous allegations of fraud and there were barely enough signatures to get it on the ballot.
UpdateGood background from the Keen News Service:
[Washington State Attorney General Robert] McKenna added, and the majority clearly agreed, that Protect Marriage plaintiffs had failed to offer any evidence to support their concern for harassment. And, noted McKenna, three other states with public disclosure laws held gay-related ballot measures and offered “no evidence…that anyone who signed any of these petitions in those three States was subjected to harassment.”There's an amicus brief about the lack of credible threats. I'll track that down and tell you about it here.
*Aside: this kind of campaign proves that it's not marriage the bad guys are after, it's any recognition of GLBT couples, because this was about DPs, NOT civil marriage. And still the right opposes it.