Here is my crude take on this. The income tax system is responsible for covering public debt _plus_ intragovernmental debt. This is why these two obligations are combined. The Social Security and Medicare program tax systems are responsible for their unfunded entitlement obligations _minus_ intragovernmental debt. This is because the intragovernmental debt for the most part represents the money that the income tax system owes to the Social Security and Medicare tax systems. The government as a whole is responsible for public debt plus unfunded entitlement obligations. This is the sum of the obligations of all the tax systems, and is clearly independent of intragovernmental debt. So whether or not you think intragovernmental debt is important depends on what you are looking at.Symbolically:
IncomeTaxDebt =PubDebt + IntraGovDebt
EntitleDebt =UnfundEnt - IntraGovDebt
TotalDebt =IncomeTaxDebt + EntitleDebt
=(PubDebt + IntraGovDebt) + (UnfundEnt - IntraGovDebt)
=PubDebt + UnfundEnt
By the way, I liked the Captcha I got:
but there are two "a"s in Klaatu. Everyone knows that.