Health-care conglomeration aligns with the Affordable Care Act, which created incentives for physicians and hospitals to work together in “accountable care organizations.” But an important and often forgotten prerequisite for this model is hospital competition.

Some see the dangers. In a rare move, Massachusetts Superior Court Judge Janet Sanders recently blocked Partners HealthCare—Harvard’s affiliated 10-hospital conglomerate and Massachusetts’ largest private employer—from acquiring three competitor hospitals. Judge Sanders argued that the expansion “would cement Partners’ already strong position in the health-care market and give it the ability, because of this market muscle, to exact higher prices.” This threat is even greater in rural areas where one hospital is often the only provider.

Today’s frenzy of hospital mergers and physician practice acquisitions is giving hospital systems even greater leverage to inflate opaque “charge-master” medical bills that even hospitals are sometimes unable to itemize sensibly. With no mechanism to allow free-market forces to keep prices in check, this translates into higher health-insurance deductibles and copays for insured Americans, and in the case of Medicare and Medicaid, higher taxes.