Billionaire Investor Warns Sports Prediction Markets Harm Men

John Arnold, the billionaire energy trader-turned-philanthropist, made his fortune by predicting the direction of markets. Now, he’s sounding the alarm on fast-growing prediction markets, saying they’re harmful to young men and boys.

His concern lies in how platforms for sports-event contracts and online betting more broadly are designed to keep users constantly engaged. Unlike traditional forms of gambling, wagers can be placed seamlessly — quickly and easily through mobile apps with direct links to bank accounts, he said. That raises the risk of addiction, particularly among young males, who are increasingly targeted by sports-betting platforms, he added.

“The sites have, deliberately ...