When are opportunity cost arguments most applicable?

Yesterday, a great many chemistry bloggers answered Mr. David Bernstein's question (posed on the Washington Post's education blog) "Why are you forcing my son to take chemistry?" I cannot really add anything to their righteous responses, so I'll send you over to Ash's, Derek's, SAO's and Janet's.

[Won't someone speak up for the joys of memorization? Very first, I assume that Mr. Bernstein is deeply mistaken about general chemistry being all memorization. Second, does anyone actually teach chemistry by memorization? Third, I've always felt that remembering something was the byproduct of actual understanding of the concept. People don't like memorizing things that are "useless" -- like the ordered list of American presidents, their parties, dates of office that I was asked to memorize as a student of AP US History (a special demand of our excellent teacher -- hello, Dr. P!) But it's only a memorized list if... you don't understand the ebb and flow of American politics. Do you memorize the alphabet, or do you understand it? Hard to say. Did I memorize Jeff Saturday's jersey number? (63, btw) Not really.]

I felt the biggest pang of potential regret when I read Mr. Bernstein's final argument:

There’s a concept in economics called “opportunity costs,” which you may not have learned about because you were taking chemistry instead of economics. Opportunity costs are the sacrifices we make when we choose one alternative over another. A family store may be turning a good profit by selling tomatoes, but it would turn a bigger profit if it used the same shelf space to sell cucumbers. There are opportunity costs of selling tomatoes. 

When you force my son to take chemistry (and several other subjects, this is not only about chemistry), you are not allowing him that same time to take a public speaking course, which he could be really good at, or music, or political science, or creative writing, or HTML coding for websites. 

Maybe he will learn something in chemistry somewhere along the way. But he will lose out on so many other more important opportunities, and so will our society, which will have deprived itself of his full contribution.

As someone who routinely uses "opportunity cost" arguments against the "STEM graduate school is good for you" meme, I am concerned that perhaps Mr. Bernstein's argument sounds a little too familiar.

But the opportunity costs of one year of high school chemistry seem relatively low. While Mr. Bernstein seems to have stipulated that it's not just about chemistry, I don't understand how it is chemistry that HAS to be the marginal class that has disallowed his son to not take a course in creative writing or HTML coding. At the same time, the relative opportunity costs of taking a Ph.D. in the sciences seem potentially very high. While we can debate the amount of time Mr. Bernstein's son might spend taking chemistry, we can all agree that a rigorous science graduate program will consume all of one's attention for at least 4 to 5 years. That you could be doing something else during that time seems apparent.

I also think there is also a distinct difference between the life of a high school student (15-18 years old) and a potential graduate student (somewhere between 22 and 28). When you're a high school student, it seems like there are very few options that you should look at and deny yourself. (Perhaps professional athlete or professional entertainer?) When you're in your late 20s, I think you should be thinking very seriously about how you will be making a living, and what your chances of success might be. Denying yourself options in high school seems a little unwise; by going to graduate school in the sciences and pursuing a doctoral degree (and beyond!), I feel that by pursuing one path (academic/industrial science), you are continually choosing not to walk other paths or raise the cost of pursuing them later.