Ok. I don't like Prop 8. I support gay marriage. I like Vaughn Walker (and, full disclosure, I have a case pending in front of him). I like Ted Olson. I still think Perry v. Schwarzenegger is a bad decision.
Judge Walker struck down Prop 8 using the test of "rational basis review," whereby a court is to defer to the lawmaker so long as there is a rational basis for the law. In practice, the categorization means that courts stay out of the question; courts don't reweigh the evidence in favor or against a legislative pronouncement, even when the legislative reasoning is foolish. Now, certainly there are normative arguments that the rational basis test should have more teeth in it than that. (Here's one.) But as a positive matter, it does not. Nevertheless, Judge Walker took evidence, and made factual findings disputing the bases for Prop 8. Objectively, these factual findings are likely correct; but there was no legal basis for the evidentiary reweighing in the first place—judges do not second-guess the legislature (or, in this case, the electorate).
Judge Walker then found that "moral disapproval" could not be a rational basis for a law. But there are lots of laws where the basis is "moral disapproval." And outside the doctrine of the right to privacy, such laws are consistently upheld by the courts. Hey, I'm a libertarian; if we're going to have a new constitutional paradigm that laws cannot be based on "moral disapproval," great, let's get rid of the anti-prostitution and gambling and bigamy laws, too, and I won't have to fly to Las Vegas to find a casino dealing double-deck blackjack. It would be hard to justify laws against dogfighting without the crutch of "moral disapproval." (And if we're going to scrutinize the purity of motivation behind enactments, then we have another reason why Obamacare is unconstitutional, as is lots of economic regulation, and the infamous Lochner case was correctly decided.)
Now, down the road, Perry will reach the Supreme Court. And when it does, circa 2012, I imagine that the Court will strike down Prop 8 and other anti-gay marriage laws by deciding that the rational-basis test does not apply to laws discriminating against homosexuals, and that the appropriate test under the Equal Protection Clause is "intermediate scrutiny," and Prop 8 will not survive that new test. (Such a decision would reconcile a number of inconsistencies in Justice Kennedy's jurisprudence, and barring any other changes in court composition between now and then, Kennedy would almost certainly be the swing vote. Nate Silver gives the good legal-realist explanation why Kennedy is going to side with the liberals—and the fact that a fifth justice could be said to think in such a lawless way puts the lie to the idea that we have a "conservative" Supreme Court.) But it will be clear that the Court is making new law in reaching that result. The Supreme Court can do that, up to a point; it can hold that it was incorrect for courts to interpret the Equal Protection Clause to permit discrimination against homosexuals, just as a few decades ago it decided that it was incorrect for courts to interpret the Equal Protection Clause to permit discrimination against women without "intermediate scrutiny." But lower courts do not have that authority.
If you want to see the difference between judicial activism and judicial restraint, take a look at a decision like Judge Posner's in Khan v. State Oil. Posner faced the same situation that Judge Walker did: irrational precedent leading to an irrational result. Posner explained at length why the precedent was incorrect, and why the result was bad. And then he followed the irrational precedent, and reached the irrational result: because only the Supreme Court can reverse a Supreme Court decision. (And, indeed, the Supreme Court "reversed" Judge Posner's ruling, and adopted instead his analysis, all the while acknowledging that Posner acted appropriately in ruling the way he did.)
Judge Walker could have written an opinion like Judge Posner's, making the same arguments, then decrying the fact that the rational-basis test permitted such a law to stand, and calling for either a stronger rational-basis test, or the use of "intermediate" or "strict" scrutiny when it came to laws that discriminated against homosexuals. But he didn't. Instead, Judge Walker misapplied precedent to reach the result he preferred. It may be the "right" result that a good philosopher-king would reach, but American judges are not empowered to act as a wise super-legislature to correct the mistakes of the other branches; the Founders explicitly rejected the idea of a judicial veto. Judge Walker is a judge, inferior in the constitutional structure to the Supreme Court, who does not have the authority to create a new constitutional paradigm.
And when judges act lawlessly to create rights they like, it means they can act lawlessly to take away rights they don't like. Just as we do not waive constitutional protections against self-incrimination and the right to a fair trial for the most egregious murderer, just as we give First Amendment protection to the most abhorrent speech, we should give appropriate judicial deference to laws we might find to be dumb. Fidelity to the constitutional structure is far more important in the long run than my personal preferences on any given issue.
See also Dale Carpenter.