1. Because all laws have issues with false/wrong accusation. So if you want to wipe out this specific one, the issue of significant numbers is important to justifying it's elimination and your proposal.
and
2. Because, you understand that otherwise, the group that benefits from your proposal is primarily those that download child pornography? This is quite straightforward. You are talking in black and white terms. Fine tune the law? Adjust the procedures involved? Sure. But if you want to talk about elimination, that's an entirely different can of worms.
The 'just one person' cliche is BS, because it deals in those absolutes. If it's either law or no law, than you have to have significant justification for the removal of it.
Otherwise the proposal is bunk, because those that primarily benefit from it are, quite simply, those that download child porn.