This is a difficult one. Implemented correctly, this kind of thing could be beneficial.
At what point does it completely undermine the referee though? Perhaps have certain technology, a referee in the stands looking at offside decisions for example could work. Take DRS in international cricket, the majority of teams review a decision for the sake of it, knowing full well it won't be successful. All that does is interrupt the game, we would have to avoid that.
Having said that, technology should be there to aid the referee, not undermine. Referees are human, we all make mistakes, as do the players; that's part of the game that we all love. Get it right, and it could be fantastic, but get it wrong and it has the potential to ruin games.