Why is it ok to use video replay in soccer after a game but not during?

Its because all the governing bodies FIFA, UEFA all the FAs etc don't understand football! They don't seem to understand that video evidence can be used throughout the game to make decisions in split seconds and this is all because they have never tried it properly. They could easily make a deal with Sky Sports or someone to do all these re plays in seconds. This would also take alot of the pressure of referees and not end up with the situation like in scotland where the refs are all about to strike due to the criticism they have recieved. I think that Fifa know its the best system but are now to scared to back track and say they were wrong!