What's to talk about? "If only the ref had seen..." is not a good basis for an argument. A game of football is not fair, and is usually decided on the strength of a handful of moments over 90 minutes, so why allow a guy who might not be near the action or who is mentally playing for a draw to interfere with these few moments?
I think the challenge system works - give the managers 3 calls, and if they're wrong they lose one. Get the stadiums to install televisions at the side of the pitch (not exactly a massive expense), and the replay will be ready by the time the 4th official has jogged over.
