Why not give the player some credit for being smart enough not to ruin the game for himself? Yes, in a perfect world you could have all the checkpoints in just the right location, but no game is perfect, and the designer can't possibly comprehend the full range of abilities and play styles and taylor their game to everyone. I think most RPG players understand that reloading convos until you get the optimal result is pointless, and constantly saving in combat makes the game too easy and not fun, but if someone wants to play that way, how does it hurt anyone else? If I really mess up in a convo and do something I didn't intend to, or if my wife starts talking to me right when I have to make a crucial decision, why shouldn't I be able to reload? I don't think the argument that if you don't have save restrictions then you shouldn't have any restrictions is valid, save anywhere is similar to having selectable difficulty levels, you can decide for yourself which policy best suits your needs.
Edit: It's a psychological effect also. Once I save, I feel confident about continuing the game, because I can't lose my progress so far. If I keep getting reset to a checkpoint, I feel like I've lost control, which starts to erode my enjoyment of the game.