It's one thing to have automated aircraft (with 'pilots' aka system managers keeping watch over systems with the possibility to change automated modes, and act as a contingency for unforseen events)
but to have nobody in the front seat would be a bit of a leap. Trusting the computers not to crash - or never to come across something unusual.
It's comforting to know there's some guy up front who has the ability to controll the plane and who has the added incentive that if he stuffs up, his fate is the same as his passengers. As it is nowadays, pilots are pretty much "Radio Transmission to Avionics actuators" for most of the time.
As it stands with current technology, Humans are good at making decisions and computers are not. Computers are great at monitoring parameters and operating controlls smoothly - but deciding to make a go around, keeping an eye on other traffic and thinking twice about possible erronious ATC instructions or instrumentation... Humans do this well, computers not so well.
There's also the "Hacker Terrorist" angle.