It's just not a good look for a trading venue to turn away orders because volume and volatility are too high. When volume and volatility are too high, that's exactly when you want to trade!
But Goldman, Credit Suisse, and UBS "told some clients to temporarily stop sending orders" to their respective dark pools yesterday as volume surged, and "a U.S. stock exchange run by Bats Global Markets Inc. had a malfunction that prompted other trading platforms to briefly stop sending orders there." So like a B+ day for the U.S. equity markets yesterday, even aside from the Athena thing. And Wells Fargo announced that it is closing its dark pool, because (1) who needs this and (2) Wells Fargo had a dark pool?