We have the technology, why not use it? Some of these arent subjective calls. So "taking the human element" out of the game is a stupid argument. The point of the officials is to make sure the game is played fairly. If they are meant to make sure that both sides play the game equally, why wouldnt it be right to aid them in doing so by using replay, especially when you have these huge screens that show it over again?
Yes, instant replay is justified, because it is a very good tool for making accurate calls. It would be a shame to have the technology available to make calls more accurate and then not use it. As long as there are limits in place to make sure that the opportunity to review is not abused, it is helpful to use reviews to make better calls.