They don't always get the calls right, but they get a lot more than they otherwise would. They don't always get them right because there is still that non-reviewable "subjective" element. (holding, pass interference, etc). I am sure that when the automobile was invented, many traditionalists of that time swore up and down that they would never need more than a horse and buggy to get around, but eventually it was accepted that technology offered a better way to do things. Change is inevitable, and if they instituted full replay next year, baseball would go on and 20 years from now it would still be going on and still be popular. Every time in professional sports something new comes around that threatens the tradition of the game; i.e, gloves back in the 1800's, helmets, smaller ballparks, biomechanics, bullpen roles, etc, people panic that it's going to ruin the game. But it never does, and as much as people complain about instant replay in the NFL, the NFL is even more popular than it was before instant replay. The strike season of 1994 season and the steroid era of the late 90's and early 2000's came and went, and the game survived, as it would survive instant replay.