This ongoing debate between [MENTION=35039]The Fish[/MENTION] and [MENTION=3566]hans kraay fan club[/MENTION] over the Shelvey / Lansbury incident shows EXACTLY why bringing in video replays for decisions on fouls during a game would be an absolute can of worms, that would cause more problems than it solves. The "right" decision is not always obvious even after several replays. It always boils down to interpretation.
Whilst I agree with you there, its not the case for a review panel, whose role is to 'overturn manifest errors', not second guess a match-day referee's valid interpretation.