我也记得是强制的

而且银行不买这个保险也没人敢在里面存钱呀

但其实不是：

The Federal Deposit Insurance Corporation (FDIC) protects consumers against loss if their bank or thrift institution fails. Not all institutions are insured by the FDIC. Eligible bank accounts are insured up to $250,000 for principal and interest. The FDIC does not insure share accounts at credit unions.