I don't think we can estimate the expected value exactly, but it nonetheless exists and our only option is to estimate it as accurately as possible (future value discounting the long term impacts of course). If the project doesn't have any practical use but opens up new avenues of research or just has value in any way then those benefits should count of course.
While I generally appreciate the way you think, the problem is likely that different people evaluate the expected value function of this project wildly differently - for perfectly legitimate reasons. The path to resolve this kind of conflict is not straightforward; barring some additional (and accepted) scientific insight, the matter is resolved politically.
