Why do stock markets end all trading for the day after a 20% fall?

The New York Stock Exchange just halted trading. This CNN entry explains the benchmarks they use to do that

The New York Stock Exchange has a series of "circuit breakers" in place to calm investors’ nerves when they’re panicked.

A circuit breaker was tripped Monday morning shortly after trading began.

The S&P 500 fell by more than 7%, halting trading for 15 minutes.

The next circuit breaker would be if the market falls by 13%. That would pause trading for another 15 minutes.

If the market plunged 20%, everyone would go home: Trading would stop for the day.

The "pauses" make sense, but the 20% "we’re done for the day" stop is new to me. What’s the rationale here? Obviously nobody likes a bear market, but why stop trading entirely for the rest of the day? Is this an SEC rule or simply something NYSE came up with? And does this really halt all stock trading everywhere, or just simply slow the process down?