Mary jokingly states that my favorite conversational comparison consists of "in theory" and "in practice." I start off talking about a principle (the "in theory" part) and how it should apply to a situation. Then I get into casuistics and how the case presents an exception to the rule (the "in practice" part). I feel like living by principle has become a reprehensible scourge in our post-modern world. Those virtues which trump all others--namely tolerance, compassion, and understanding--don't fit into the principled world-view.
It can be excruciatingly difficult to live by principles. A life devoid of principles is a life driven by a subjective, ad hoc, set of values that fundamentally alters anytime it's convenient.
Philosophy typically divides the world into three categories: being, thought, and action. Each category is fundamentally different. The United States judicial system is prosecuting those individuals whose actions go against an established law. Our laws establish what we can do and what we can't do: they don't establish what we can think and can't think. It's not the place of any government or institution to dictate our thoughts. Individual rational thought is an essential part of the human person. "Nuf said."
While thought-crimes exist in various parts of the world, I don't know of any precedents where thought-crimes have been prosecuted. Recently, however, law enforcement agencies are moving in the direction of punishing thought-crimes in the U.S. In a pluralistic country such as the United States, every opinion or world-view should possess equal value and validity. Yet, it's becoming increasingly dangerous to adopt controversial/marginal opinions. While I disagree with pedophilia in principle and practice, should law enforcement agencies restrict American citizen activities simply based on ones thoughts? As attested in this article, many think so. I disagree. A society that is truly pluralistic must in theory and in practice rank all opinions as equal. Like I was saying before, it can be tough to apply good principles to all circumstances.
(For what it's worth, I personally don't think that countries should be as pluralistic as the U.S. I think that pluralism is a good thing but within certain parameters. National constitutions should provide those healthy parameters that, by nature, will be discriminatory. For instance, insofar as the U.S. constitution mentions God, it discriminates against atheists.)
At a personal level it can also be difficult to apply principles of discipline to our kids. We have to pray for the strength to cling to our principles in all times...even when the going gets tough.