Medicare, Social Security and the like are special cases, because they are effectively more investment trust funds than the taxes they nominally are. Past debates over whether SS etc. are "taxes" require I state this very carefully, but you know what I mean, I am sure. People who live long enough (theoretically) get back—with interest—every dime paid into SS and Medicare; SS withholding is capped partly for that reason. Medicare and SS were not meant to finance government (even though SS did just that for a generation, until its balance finally became negative last year; now we have a BIG problem amounting to about 15% of our federal debt by itself.)

It is fair to not count such things as the nominal "tax" they are, since they only represent entitlements held in trust, to be later returned to taxpayers. They reduce the amount of money people have to pay bills today, but only in exchange for increasing money available for that tomorrow. They do nothing to support national government. It is reasonable to say people who only pay SS and Medicare taxes do not pay part of the countrys costs, because it is true. There is a very good reason for that (i.e. they cannot,) but the statement is essentially sound.