How many times do we have to see prosecutors using laws in ways never intended when passed before we stop passing these broad laws?

After Enron anyone fighting against Sarbanes-Oxley passage was laughed at for claiming it was over-broad. No prosecutor would misuse it, of course it's just meant to reign in other evil doers like Enron.

Why is it that anyone even considers the idea that we can rely on proprietorial discretion to keep laws in check? Shouldn't that concept be laughable by now?