The current proposed expanded replay system is 1 challenge throughout the first 6 innings and 2 challenges from the 7th inning on. However, if you get a challenge right, you don't use up your challenge. This means that managers will get a minimum of 3 challenges a game in a sport where we see at most 2 game-changing missed calls in a game. If challenges got used up when used successfully, then we'd have strategy in deciding when the most efficient time to use challenges is. More strategy makes the sport more entertaining. The bottom line is that baseball is for entertainment, so whatever option is more fun for the fans is the one you should go with. With expanded replay, we won't have manager arguments anymore because they'll just challenge instead of arguing (unless they used up all their challenges, but this won't happen because there's too many challenges). Manager arguments are entertaining, so it's bad for the sport to get rid of them.
The proposed replay system has more challenges in the end of the game than the beginning, implying that the end of the game has more game-changing moments than the beginning. This just isn't true. They should make it 1 challenge through the first 5 and 1 challenge onward, and remove the ability to retain challenges when successful. Or, just make it 1 challenge for the entire game. Most games have between 0 to 1 blown calls that affect who wins, so even one challenge per game would be more than enough. Baseball has a massive 162 game season, so even without expanded replay it's still the fairest sport in the world for deciding who rightfully makes the playoffs. I don't think we should remove a big chunk of baseball's character (manager arguments and controversy) and make the game more boring just to make the standings slightly more fair. Discussing how expanded replay should work in the playoffs is a totally different topic.
I don't have a proven-correct opinion about this, but my point is that it's far from a no-brainer to accept the proposed replay system.