YOU CAN UNDERSTAND Ed Robinson’s frustration. Our state’s sales tax is riddled with 61 separate loopholes — just about every kind of service you can think of goes untaxed. And yet his profession — dry cleaning — has to charge its customers a sales tax.

Last week’s ruling by the state Supreme Court, upholding the General Assembly’s right to create a swiss cheese tax code, ends Mr. Robinson’s quest to have the courts grant him an exemption that lawmakers have refused to grant. But it doesn’t, or at least it shouldn’t, put the topic to rest. Rather, this case serves as yet another reminder of just incoherent our tax code is.

The problems run throughout our entire tax system, which has been amended in bits and pieces with special exemptions and exclusions and credits designed to mollify whatever interest was screaming loudest at the moment. Nowhere are these problems more apparent, though, than in the sales tax law:

We tax wheelchairs and eyeglasses but not prosthetic devices and hearing aids, aspirin but not prescription pain-relievers, Prilosec but not Nexium.

Retail and service businesses pay a tax on their electricity, but homeowners and most manufacturers don’t.

We tax clothing you wear to work or school or anywhere else, unless you happen to work in a “clean room environment,” in which case there’s no tax.

Free clinics have to pay a sales tax on cars and other personal property, but hospitals whose mission is providing free care just to children don’t have to.

We tax hotel rooms but not vacation time-shares.

We tax paving materials if they’re used here but not if they’re purchased here and used in other states.

We tax cell phone service and intrastate long distance, but we don’t tax interstate long distance or toll charges between telephone exchanges.

We tax baby-sitting services but not diaper services, health club memberships but not dance lessons.

We tax $6,000 clunkers at 5 percent, but tax $60,000 luxury cars at one half of 1 percent.

Even in finding the tax code constitutional, the justices agreed that Mr. Robinson “may be correct in noting such exemptions belie a misunderstanding of economics, and are therefore unwise in an economic sense.” Chief Justice Jean Toal, in a dissent, went further, arguing that while the state “attempted to pigeonhole 33 of the exemptions into six neat categories for tax classification purposes ... the whimsical nature of the other 28 exemptions renders this legislation arbitrary and capricious.”

The constitutionality of the system is now settled law. The justification for it is not settled. The rationality of it is not settled. Nor can they be, because the system is neither justifiable nor rational. A tax code shouldn’t be based on who can hire the best lobbyist or scare the most legislators. It should be based on such principles as spreading the tax burden widely and thinly, concentrating on the taxes the public considers most fair and least objectionable, and balancing various taxes so changes in the economy don’t cause drastic increases or decreases in collections. It should be stingy with exemptions, granting them only as needed to encourage the types of behaviors we mean to encourage.

Our tax code was not built that way, nor does it reflect those priorities. Indeed, our tax system is so far from that ideal that the only way we can achieve it is to scrap the entire thing and build a new one from scratch.