There's no more of a problem with Treasury and the Internal Revenue Service making public policy than there is with any other government agency making public policy. And the extent to which you find policymaking by government agencies to be troubling is dependent upon your perspective. We've had executive branch policy making since the beginning of the republic.. Statutory text by its very nature is going to contain some amount of ambiguity. In order to execute the law, the executive branch has always had to interpret statutory text even when that text is ambiguous. It has to decide how to apply statutory text to facts and circumstances that perhaps deviate from the paradigmatic example that Congress had in mind when it adopted that statutory text in the first place. Now, that may be small “P” policy, but it is nevertheless policy making. Of course, in contemporary times, Congress explicitly in some instances through specific authority rule making grants; implicitly in other cases where you have ambiguous statutory text coupled with a general authority grant of rule making power has delegated a lot more authority to federal government agencies including but not limited to the Treasury Department and the Internal Revenue Service than perhaps was delegated at the time of the founding. But the question becomes, is that a matter of degree or a matter of kind? And that's a question that simply doesn't have a clear answer. In fact, the answer really falls more along a continuum than representing a binary choice.