What is the beef with School League Tables?

In all seriousness... it's only because I can't see the problem with a publishing of 'League Tables' of schools and their performances.

Sure, I get not publishing class photos, and I understand that rating schools against each other (in a simplistic context) can give an exagerrated view of the school's overall performance. However, shouldn't parents be able to compare schools and see just where performance is falling down?

...or am I missing something?