In this day and age with the slow motion instant replay, we have the advantage of hindsight. Being able to challenge mistakes is a good thing in some ways. But the slippery slope it causes may not be. With the NFL allowing challenges on PI we're going to have to see if that doesn't become part of the game strategy.
How many successful challenges will there be on hail mary's? On calls that would never be made without the challenges? We all know there is some sort of contact on those plays. If a team wins a game or scores a TD before the half on a challenge, I can see teams working that in their game plans. Have the receivers initiate contact with their body and get a call.
I notice watching MLB they have the strike zone for the viewers. Sometimes the ball isn't in that zone and its called a strike. Sometimes its in the zone and its called a ball. As long as the umpire is consistent with those calls I'm fine with that. I'd hate to see strikes and balls being called by technology instead of a live human. Part of the strategy for pitchers is knowing a particular umps strike zone and working with it. One thing though that really ticks them off is when the ump changes his zone later in the game.