There are also appropriate levels of caution. Shutting down the world was not an appropriate level of caution.
Also, without being able to test the entire world, you're basically just sitting and waiting for the government man on the TV to tell you you're safe. Have you ever thought about how irrational that is? I mean let's face it, they're going to open back up without actually knowing how many infected are still out there, since testing the entire world, or even an entire country, is not realistic. For the majority of people, they're going to be in as much of the dark now, as they will be when they're told to get back out there, and the only reasoning they will have for feeling secure, is that the government man on the TV told them it's okay now.