A number of pundits have been trying to explain why Republican presidential candidates are increasingly dabbling in birtherism. Paul Waldman, for instance, has developed a fascinating theory of a loop: Tea Partiers are increasingly convinced that Obama must not be American precisely because reporters and liberals continue to insist otherwise — and conservative politicians must respond in kind.

But there’s another reason the 2012 GOP hopefuls are dabbling in birtherism: It’s a policy-free way to pander to a group of voters that holds some highly unpopular positions on issues of public policy — positions they don’t want to espouse themselves.

In that, birtherism is exactly like the Balanced Budget Amendment that Senate Republicans are rolling out. That largely symbolic Amendment is a terrible idea, even for those who care about deficts; the way to balance the budget is to increase revenue or decrease spending, and all the procedural tricks in the world won’t substitute for that. But spending on specific programs is popular, especially among swing voters, and tax increases are unpopular — especially among Republican activists. So the safer course is to support a handful of minor cuts and a major symbolic measure.

Birtherism — especially what Adam Serwer calls “ironic post-birtherism,” in which a politician uses jokes to establish a shared point of view about the illegitimacy of Barack Obama’s presidency — works the same way. Tea Partiers and other movement conservatives hold a variety of wacky and extreme positions on issues that mainstream presidential candidates, even very conservative ones, wouldn’t want to touch.

So instead of opposing the direct election of Senators, or supporting the elimination of several popular cabinet departments, or campaigning on nullification — all of which would be difficult to defend in a general election campaign and would alienate middle of the road voters — it’s much easier for presidential candidates to make jokes about Kenya or birth certificates. It’s a cost-free way of signaling similar political sympathies without having to be held accountable later for your positions on issues.

The question remains whether the committed movement conservatives who vote in primaries will be satisfied by symbolic politics, or whether they’re going to insist on pinning candidates down on substance. We’ll find out next year in Iowa and New Hampshire.