I think the rule is actually very sensible. Before this rule came in, some players used to write down alternative moves for their next move and then mentally check through each alternative before deciding on their move. They then crossed out the alternatives on their scoresheet and finally played their move. They were therefore using their scoresheet as an aid to their thinking process.

There was nothing to stop players writing down not just possible moves, but also variations - they could always claim that they were just writing down a possible next move and made a mistake.

I suppose it could be argued that the situation was equal for both players, but it goes against the principle that players should not use an aid to assist their thinking and also resulted in some very messy and often illegible scoresheets.