U.S. District Court Judge Vaughn Walker, a Republican appointee who is presiding over the trial in the federal legal challenge to Prop 8, has been asking lawyers and witnesses versions of the same question, over and over again. Why is the state involved in sanctioning marriages anyway?

These queries, which seem to spring from a libertarian perspective, might seem harmless, and suggest the judge is sympathetic to the cause of marriage equality. But the judge’s questions should make supporters of same-sex marriage nervous.

It’s because the judge is trumpeting one of the most frivolous – and thus dangerous – ideas in the debate over same-sex marriage. Let’s just take the government out of the marriage business.

This is a bad idea for two reasons. First, marriage is both a private and a public institution, with a long history. It’s a tradition at the center of family life, and thus a lot of law. Upending that would create change and turmoil that goes far beyond same-sex marriage. As such, to decouple the government from marriage is a radical notion. Legalizing same-sex marriage, in contrast, isn’t particularly radical at all. It extends marriage, with all history and traditions, to a small percentage of the population.

Which is why, if Walker were to embrace the libertarian separation of marriage and government in a court decision, the second problem with his idea would quickly become apparent. His notion is an enormous political threat to the cause of marriage equality for gay couples.

How’s that? One of the most important political and legal arguments in favor of same-sex marriage is that it doesn’t hurt anyone—no one’s marriage is at risk as a result of expanding existing marriage rights to gay couples. In court, Prop 8’s defenders have had a difficult time identifying any harm to society from same-sex marriage. But Walker’s perspective, if turned into legal precedent, does threaten other people’s marriages – particularly the marriages of secular straight couples who wouldn’t want to get married in a church.

I consider myself a strong supporter of marriage equality, but as I’ve written previously in this space, a Walker-like decision would turn me into a reluctant opponent of same-sex marriage if its effect were to limit the ability of people – particularly those without religious affiliation – to have their marriages recognized and recorded by the state. It’s political poison to link the cause of marriage equality with the taking away of existing marriage rights and traditions.

Supporters of marriage equality, including Ted Olson and the team of lawyers arguing against Prop 8 in court, need to make their opposition to Walker’s thinking in this matter clearer.