I'm not sure what specific law you are talking about, but I'll hazard a guess and say that it probably isn't a specific provision regarding protection of priests who engage in sexual assault.  But I can understand canon law that seeks to insulate itself from secular laws, so maybe we're not talking about the law, per se, but how the law is being misused/abused.

St. Peter Damian had a lot to say about infiltration of the priesthood by homosexuals and pedophiles, but I don't hear too many railing about how canon law seems to be protecting homosexuals, so again, this sounds like selective use of canon law.