Originally the question was raised by a Christian minister in a class on world religions. The text book in that class translated moderation as "the middle way", which the minister felt was an outdated idea with little contemporary relevance. For instance, how do you decide on the issue of abortion halfway down the middle using this principle? Surely aborting half a baby would be absurd!
I'm glad this question came up. It tells me that there is still much misunderstanding out there about the wisdom of the sages. It also demonstrates the importance of our mission - to disseminate the true Tao in this society which seems fascinated with Chinese philosophy, and yet falls short of really comprehending its truths.
In this case, the root of the misinterpretation lies in the unfortunate "middle way" translation, which may be the work of someone who is not a native speaker. As we survey English literature on Tao and Zen teachings, we see this is a rather common problem. It's entirely possible that a reader who learns through these imperfect translations will get the same impression as the minister - that such teachings may have been useful in a simpler past, but cannot address the complexity of our present.
Those who know the teachings in their original Chinese know that this isn't so. The sages spoke of enduring truths, of basic concepts that remained constant with the passage of time. The Sun rises today and will continue to do so tomorrow and the day after, just as it has for countless generations past. For the same reason, we say that the Tao is eternal - it is, essentially, a fundamental feature of human existence.
So how do we apply the concept of moderation to modern issues like abortion? It is simple once we understand that the spirit of moderation is the avoidance of extremes and striking a balance somewhere between the two ends of a spectrum. Why is that important? Because extremist views lead to fanaticism and zealotry, which bring all kinds of negative baggage like limiting beliefs and narrow-mindedness.
So what are the extremist views when it comes to abortion? We have radical factions in both the pro-life side and the pro-choice side. Extreme pro-lifers, often associated with the religious right, believe the fetus constitutes human life from the moment of conception, and since only the Christian God has the right to take human life, any abortion at any time during pregnancy is equivalent to murder. On the other end of the spectrum, those who subscribe to radical, militant feminist pro-choice views believe the human choice reigns supreme, so that even an abortion decided minutes before delivery isn't morally wrong.
The above are, of course, drastically simplified from complex issues. Nevertheless, it should be obvious by now that most of us find the extremes contrary to our intuition. The pro-life extreme, for instance, make no exception for cases where the mother is the victim of rape. Similarly, we don't care much for the extreme pro-choice idea that people can just act without regard to consequences and utilize abortion as a form of contraception, as if child-bearing is a game!
So if moderation avoids both extremes, what does it teach us about this issue? It does not give us dogmatic rules that we must follow in every instance. Such rules would be the product of lesser minds than the ancient philosophers we study. What the principle of moderation says, very simply, is that every case is unique and must be decided upon its own merits and circumstances. Sometimes abortion is the right thing to do, and sometimes it is wrong. It isn't aborting half a baby or vacillate between two extremes. There is no literal "middle way" like a fine line down the exact center in the philosophy of moderation.
You may find yourself thinking, "But that is too simple!" If so, it means we're on the right track. Remember our discussion on the idea of PUPS, the common attributes we find in all great truths - Powerful, Universal, Profound and most of all Simple. This kind of simplicity, once understood, resonates deeply within our intuitive mind. We say that it has "the ring of truth."
The principle of moderation rings true. We can apply it to any conceivable issue in the world of today and tomorrow. When used as a guide, it steers us toward wisdom and away from the lunatic fringe. In order to answer the question, "Is the principle of moderation applicable in the modern world?", we only need to ask, "Are there extremist, fanatical, and closed-minded views in the modern world?" Our answer is the same to both.