Supporters of the bipartisan immigration reform bill being debated in the Senate got a shot in the arm yesterday when the Congressional Budget Office issued a report that did no more than verify what has always been the commonsense position on the issue. Fixing a failed system that could bring millions of much needed workers out of the shadows and into the federal tax regime will be a net plus for the government’s bottom line. Reform will bring in hundreds of billions in revenue to Washington due to a work force that will be bolstered by a new guest worker program as well as the ability of currently undocumented aliens to take part in economic activity in ways currently impossible. Even in the second decade after adoption of the reform package when currently illegal residents become eligible for government benefits, their positive impact on the country’s fiscal health will outweigh any outlays. As Representative Paul Ryan said today, immigration is vital to America’s future economic health as our population ages, making passage of a reform package—whether the gang of eight’s Senate bill or a House version—imperative.

But don’t expect the CBO to influence the conservative activists deluging Republican senators and House members with messages urging them to defeat the plan. Much of the party’s grass roots are so committed to the idea that any path to citizenship is an outrage that they are not likely to listen to reason about immigration’s impact on the economy any more than they are to those that point out that it is foolish to think the 11 million illegals in the country can be deported. The gang of eight’s bill may not be perfect, but it is rooted in a decision to face reality about our current situation that has not been matched by any compelling points in the responses being mustered against it. Whatever the outcome of this debate, the willingness of so many Republicans to associate themselves with arguments that seem to align them with those who oppose immigration in principle is a huge potential problem for the party. If gang members are reluctant to alter the bill to make it more acceptable to opponents, it’s because it’s increasingly clear that a lot of those complaining about it wouldn’t be satisfied with anything but the construction of a 700-foot-tall ice wall along the border with Mexico just like the one in the popular Game of Thrones show on HBO whose purpose is to keep out zombies.

Part of the reaction to the CBO report is based in understandable skepticism. Republicans are used to taking the CBO’s pronouncements with a grain or two of salt and trusting what groups like the Heritage Foundation take as gospel. But there was a reason why Heritage’s report that attempted to claim that immigration reform would bury the government in debt wasn’t taken seriously by most observers. As Seth noted last month, Heritage’s claims—which are being echoed again today by some reform opponents—were mainly an argument about entitlement reform, not immigration. Heritage’s numbers didn’t make sense. There is a reason why the business community has always favored immigration. It’s always been good for the economy and no amount of grousing about the details of this bill or about an entitlement system that is in desperate need of reform changes that.

But, like the unfortunate tendency of some on the right to claim that the real problem with immigration reform is that it will create more Hispanic voters who will become Democrats, the reaction to the CBO is revealing the discomfort that some people have with legal immigration. If, as the Daily Caller reports, some on the right are scared by the idea that reform will create a wave of immigration that they wrongly think would be bad for America, then this debate is turning on sentiments that are neither defensible nor logical.

Reform skeptics have a strong case when they ask for the bill’s provisions on border security to be strengthened. But if this issue is driven not so much by concern that illegal immigration will continue but about the identity of those who are in this country legally in the years to come, then those Republicans who buy into this line will be venturing out onto thin ice.

Let’s be honest, if you are scared by the idea of a large number of immigrants coming to this country in the future, even if the vast majority of them are arriving legally, then it’s time to admit that this dispute isn’t about the rule of law or amnesty, but something else than isn’t nearly as attractive. What Republicans like Paul Ryan and Marco Rubio are putting forward is a positive, pro-growth vision of the American economy that has always been part of the GOP vision. If, as seems increasingly likely, Republicans sink immigration reform because of fears about it giving the Democrats a political advantage or because they are just not comfortable with expanding America’s population, then that is both bad policy and bad politics.