Why would you do that when they aren't contagious?
Because once you know that they are, if they were in contact with other people, it might have been transmitted?
I agree it is overkill in the sense that, realistically, you can *probably* be sitting next to someone on a flight from cleveland to denver (or wherever) who has ebola, and a fever to go along with it, and not catch it, as ebola is, as has been mentioned above, not a particularly contagious virus. But that chance certainly isn't zero. And yes, we don't want to spend absurd amounts of time, money, trampling civil liberties of thousands, etc, on worthless what-if type scenarios. But that chance I mentioned above is certainly important enough that the CDC has tried to contact everyone who may have been around the nurse on the flight; if someone who starts to develop symptoms is at work, do they magically teleport to home? what if they used the bathroom? how clean are the faucet handles, really?
Would they spread ebola if this occurred (become symptomatic at work)? perhaps, probably not. Perhaps by something like 99.9%, probably not. But if that .1% chance can be avoided by watching movies for three weeks, is that really an absurd idea to consider?
The idea isn't to quarantine people who aren't contagious.....it is to quarantine them before they become contagious, so that if they do become contagious, it does not spread.