(Bloomberg View) —In the tradition of turning swords into plowshares, it’s an appealing idea: converting the U.S.’s ballistic missiles into rockets for civilian space transport. It’s also a sensible one — and Congress should change the law to make it happen.

For two decades, on national security grounds, Congress has barred the sales of parts of decommissioned intercontinental ballistic missiles such as the Minuteman III. The collapse of the Soviet Union and ensuing arms treaties resulted in hundreds of ICBMs being decommissioned and stripped of their nuclear warheads; many of them remain underground in their old bunkers in the Great Plains. Now, as part of a $355 billion refurbishment of the U.S. nuclear arsenal, these missiles will be destroyed and replaced with a next-generation ICBM.

One defense contractor, Orbital ATK, says it wants to recycle the propulsion systems of those missiles and use them to launch commercial satellites. This would give taxpayers some return on the billions of dollars the Pentagon has already spent and save the cost of destroying them. It is asking Congress to overturn the sales ban.

Orbital’s suggestion has met with resistance from the commercial spaceflight lobby. The government’s very own policy requires it to encourage “a competitive commercial space transportation industry,” they point out, and not to compete against U.S. private-sector firms. They say the sale of these rocket parts would undermine a nascent but vibrant sector of the aerospace industry.

But there is no convincing case that reselling the ICBM parts would harm the newer private companies pioneering space travel. Orbital says that the sorts of large-scale cargo missions for which these motors would be appropriate are a different business from the smaller satellite launches that are a focus of companies such as Virgin Galactic, SpaceX and Blue Origin. Moreover, the Air Force has indicated that it would not dump the rocket motors onto the commercial market.

At any rate, all this may be premature: It’s not yet clear that it makes economic sense for any private firm to buy one of these motors. Or that adapting ICBMs for commercial use is technologically feasible (although Orbital already uses old motors for launching government payloads, and Russia has made a business of recycling its defunct missiles). There is also no real estimate of how much they would sell for.

The market can provide answers to some of these questions, especially about price. But as long as Congress maintains its ban on the very idea, we’ll never know. And if it turns out to be a sensible investment for the private sector, Virgin Galactic and other competitors are welcome to get in on the bidding.

Besides, it’s not as if Virgin Galactic and similar firms — SpaceX, Blue Origin — aren’t already getting government subsidies. Some wouldn’t have viable business models without the government as a major client. They don’t need protection from Congress.