Analysts played down the threat to the U.S. banking system after the collapse of a regional lender Friday, but the failure of Silicon Valley Bank served to underline longstanding worries that the Federal Reserve’s aggressive series of interest rate hikes will eventually cause something in the world’s financial plumbing to break.

And so, U.S. stocks closed sharply lower Friday, posting big weekly losses and nearly wiping out a year-to-date gain for the S&P 500 SPX. Underscoring the worry, investors continued to pile into safe-haven…