SAUDI ARABIA'S Crown Prince Mohammed bin Salman wants to shake up the hidebound kingdom. He has already announced that women will be permitted to drive, launched an anti-corruption campaign, allowed movie theaters to open next year, imposed budget austerity and revealed expansive ambitions to diversify the economy away from its dependence on oil. All this seems responsive to a restive younger generation. But the crown prince has occluded his vision with a taste for grandeur.

He reportedly bought a luxury chateau for more than $300 million in Louveciennes, France, near Versailles, and he acquired a 440-foot yacht from a Russian tycoon in 2015 for about $550 million. Those prices are eye-watering, but the Saudi government says the crown prince did not provide $450.3 million for the most expensive art purchase in history, a Leonardo da Vinci painting recently sold at auction.

Certainly, the anti-corruption campaign, in which 159 of the kingdom's richest businessmen, princes and officials were rounded up and detained at a five-star Ritz-Carlton Hotel last month, had more than a whiff of a power grab. The corruption problem is real, and so is the impatience of the younger generation. But don't look for trials for those detained in their cushy suites. Instead, the crown prince is attempting to coerce the wealthy into signing over tens of billions of dollars in assets to avoid prosecution and win their freedom. This is a crude method of an autocratic regime, not a modern rule-of-law state.

Why did the crown prince, railing against self- ­enrichment by his peers and colleagues, decide to plunk down more than half a billion dollars for the mega-yacht and the villa in France, which sits on a 57-acre landscaped park? The chateau was completed in 2009 with a 17th-century design but modern technology, according to the New York Times: "The fountains, sound system, lights and whisper-silent air conditioning can all be controlled remotely by iPhone." Nice. But the symbolism is awful and suggests the crown prince has one vision for his people and another for himself.

If he is truly interested in demonstrating enlightened and modern leadership, he should unlock the prison doors behind which he and his predecessors have unjustly jailed people of creativity, especially writers critical of the regime and intolerant religious hard-liners. Recently, he oversaw a crackdown that swept up influential clerics, activists, journalists and writers on vague charges of endangering national security. Allowing these voices to thrive and exist in the open would be a real contribution to the kind of society he says he wants. In particular, he should arrange an immediate pardon for blogger Raif Badawi, serving a 10-year jail sentence in the kingdom for the crime of free expression. Mr. Badawi offended hard-liners when he wrote that he longed for a more liberal Saudi society, saying, "Liberalism simply means, live and let live."

Opening Mr. Badawi's cell door would do more to change Saudi Arabia than purchasing a fancy yacht and a villa in France.