Jim Bianco, founder of Bianco Research, criticizes the recent popularity of spot Bitcoin ETFs, suggesting they may hinder the growth of a decentralized financial system. He highlights that only 3% of these ETFs are held by investment advisors, with the majority held by retail investors, indicating a lack of institutional interest. Bianco also warns that these ETFs could cannibalize on-chain volume, as evidenced by Coinbase's Q1 earnings report.