Feedback on Ref decisions

This is something we really need, during a match we hear "Player X is furious with the ref", "He claims player X handled the ball". How are we meant to know whether or not to disagree? You can't see this on the replays and in real life a manager would be able to see this before making a comment.

Also why do the FA warn you for disagreeing with a refs decision? In real life a manager is allowed to disagree with decisions, it's just they're not allowed to suggest that the ref was biased or unfit.