It sounds vaguely plausible, but it is totally wrong. Reading Michael J. Perry this week has brought home to me even more strongly just how wrong it is. What our religious friends often mean by "separation of church and state" is that the state does not interfere with the activities of the church, but the church is free to persuade the state to impose a religion-based morality on the citizens - including (or especially!) citizens who reject that morality. With relatively minor qualifications, Perry argues for something like this, as do other high-profile Christian scholars working in such areas as legal philosophy and constitutional law. Less erudite versions of the same doctrine are widely adopted by Christian leaders from the Pope down and accepted by ordinary Christians. This is the real world that we live in, a world where there is no consensus for accepting the harm principle and other liberal principles (and where such phrases as "freedom of religion" can be given Orwellian meanings by people who wield power and influence).
I think this is an absurd and unfair interpretation of the idea of separation of church and state, but that's not the point. In the real world, politicians often do use the law to impose their specifically religious morality, in the absence of any strong or even plausible secular case for what they propose to do. They do so with a clear conscience, believing that this is legitimate. Many lobbyists and electors applaud, and even urge them on. And that means that it is, at least covertly, always an election issue just which religious morality if any is actually correct. Which further necessitates that there is no choice but to enter into arguments about whether the holy book that a religious morality comes from really is divinely inspired ...or whether it is a human construction entrenching many of the barbaric moral assumptions of an earlier time. In the real world, we have no choice but to scrutinise the claims of religion and persuade as many people as possible that those claims are actually false, or at least doubtful. I wish there were less urgency about this, and that we could all be nicer about it, but that's not the world we live in.