In today's economy, banking -- and by that I mean the basic function of a secure place to put your cash other than having it in dollar bills in a safety deposit box or under a mattress -- may be considered an "essential service", particularly for businesses. The fact is, you cannot operate a business without it. So putting your money somewhere safe (I'm talking cash here, not investments) should be something that is guaranteed. The $250K limit does that for individuals but not for businesses who may need millions in readily-available zero-risk (other than inflation) cash.

This line of thinking leads towards basic banking services being fully guaranteed, and perhaps owned, by the government (like the postal bank in some countries). Banks make money by providing other services on top of that.

Something along the lines of how power utilities work might be a model for the future.