Rules or Principles?

The Wall Street Journal poses the question with regard to regulating the financial industry. It's clear that principles grant more potential for good decision-making. However, rules have a place too. There are some actions that ought simply to be prohibited. But principles are better at capturing the spirit of the law--rather than its technical fact.
What's interesting is that, in the article, the advocate for principle-based regulation argues in black and white terms--as though a blend is not a feasible option. That sounds rather like the very problem with rule-based regulation -- it leaves no room for nuance. Irony reigns supreme.