Here’s a parody of a calculus problem for you.
dQ/dt = du/dt  di/dt + M
I don’t know how to solve it but I know enough to know it’s not really
a proper calculus problem. In this equation Q
is quality of life,
u
is the utility of calculus, and i
is the investment one makes in
developing a calculus proficiency sufficient for u
. M
is the
intrinsic motivation to learn and be knowledgeable about calculus;
mine is used up! Although this equation is quite silly it parallels
all real world textbook problems involving calculus by distorting the
situation into an absurd simplification.
I consider this equation a very dubious justification for the
extraordinary emphasis placed on calculus in the educational system I
was (and still am) a part of. For me, calculus was no small investment
(i
). Between high school calculus and a university engineering
degree, I was studying calculus for about 3 solid years. And although
I don’t have a typical engineering career, I am horrified that I have
put my calculus training to good practical use exactly zero times in my
life (u
). The reason for this, perhaps the reason I intuitively let
myself not be as proficient at calculus as possible, is that I believe
that calculus is never essential if you have access to a computer. And
if you do have access to a computer (which is everybody reading this),
calculus is actually irritatingly counterintuitive because it implies
some wrongish things about how to best model the world (an assumption
of analog, for example). I’m not talking about using a computer
instead of calculus to "get answers" the way a pocket calculator
(app?) can do basic arithmetic. A pocket calculator does not replace
the need to understand arithmetic but numerical solutions with a
computer do obviate the need to understand calculus.
Hokey religions and ancient weapons are no match for a good blaster.
Apologists argue that calculus may not be super useful but that the equation above is close enough that a radical restructuring of education wouldn’t be worth a mere quibble. The problem with this equation, however, is that it is missing a very important term. Here’s the better version.
dQ/dt = du/dt  di/dt  dc/dt + M
Here c
represents
opportunity costs. In
less economic terms, critics of calculus must answer the question,
"What should we be teaching/learning instead?" There is no argument
that calculus is useful. It is, just not very. This implies there are
better ways to spend our time. There are, many. Besides potential
engineers and physicists, I can’t think of any reason for high
school students to learn calculus that is better than the reasons to
learn the following things.

Vocational (machining, welding, plastics, ag)  Even if you aren’t going to fix your own car or work in a factory, understanding the foundations of the most real parts of our civilization can’t possibly be a complete waste of time. If I had to relinquish either my machine shop apprenticeship or my university engineering education, I would jettison the latter.

Language History  This is commonly called "Latin", but really learning some Old English and Latin and how English became to be like it is (throw in King James, Shakespeare, etc) turns out to be extremely useful in building solid communication skills. Many foreign speaking cultures now teach their kids English well enough to smoothly participate in the Anglosphere. Language history would help English speakers preserve an edge. For the same reason, I would mention enhanced grammar study as being much more useful than calculus but I understand that, unlike the colorful history of language, it’s only slightly more interesting.

Art  Did you know that the BLS predicts that by 2024 "Arts, design, entertainment, sports, and media occupations" will increase by 4.1% (source)? Despite wasting so much of my life learning calculus I have enough math sense to notice that because the percent increase in total occupations is 6.5%, this is actually a per capita net loss. So we really should be focusing on engineering, right? Uh… No. That is projected to grow at only 2.7%. That’s 50% more of a reason to support the arts over engineering. The US is a world leader in design, fashion, fine art, graphic art, digital art, performing art, movies, video games, photography, cuisine, typography, and sports. All despite calculus. We could reinvest in our waning art culture or leave it to other cultures to take over.

Music  And if American art has been a grand success, America has been to music what the 13th century Mongols were to Asia. Calculus is probably best learned well into adulthood if the need arises. Music is best learned when young. We neglect our true cultural legacy at our peril.

Home Economics  Are our real problems today a lack of people who can derive formulae for ballistics trajectories using 18th century techniques? Or is it that as a species we’re all becoming depressingly unhealthy and fat? Empowering high scholars to make better decisions about food would surely pay society back far more than calculus. Or maybe offer kids the option of an hour of running or an hour of calculus lessons  obesity epidemic cured!

Personal Finance  How about helping hapless high school seniors out with the facts of life about debt before they take on those predatory student loans. And credit card debt, payday loans, adjustable rate mortgages, etc. To give them calculus instead is a shameful dirty trick.

Statistics  Proponents claim calculus is good mental exercise for later skills in technical fields that are essential. They also say the history of calculus is important for understanding modern technology. That’s fine, but the warm up doesn’t also have to be useless and disorienting. I have a lot of problems with statistics as it’s normally taught (I had almost 2 solid years of that), but even if it’s all completely bogus, it’s still topical and essential for engaged discourse. Who knows, maybe if we treat it seriously we’ll produce an Einstein type figure who will revolutionize the field and create a paradigm shift appropriate for the modern uses (e.g. quantum physics) which Bernoulli, Laplace, Gauss, and other early pioneers had no intention of contributing to.

Linear Algebra  "Think of the engineers!" cry the calculus apologists. Surely they need all this "math" just for good practice and it just might be useful. Bollocks. If we care about that, linear algebra is the way to go. If you’re an engineer in 2016 and you’re using Newtonian calculus way more than linear algebra, you’re doing it wrong. In fact, if you’re doing something serious and you’re not using linear algebra to do your Newtonian calculus you’re probably doing that wrong. Linear algebra has the delightful bonus property that it teaches itself to many adolescents (and adults)  "Hey, who’d like to make a 3d video game?"

Numerical Analysis  Less interesting than linear algebra but way more useful than calculus is numerical analysis. If we’re compulsively fetishizing the cult of personality of Sir Isaac then numerical analysis is ideal.

Information Theory  "No, no, we need calculus because $BetterAlternative is too easy." If this is your feeling, that high school kids need to be tormented with a weird subject that is incomprehensible in any way to normal people, then information theory is ironically hard to communicate to students. Honestly, it’s not a great idea to add information theory to a standard high school curriculum but it would be much better (useful/interesting) than calculus! If we could just broadly teach people that "password" is not a good password, it’d be a good trade.

Computer Science/Programming  It may not have been obvious in 1953 when the first transistorized computers were built that we, as a society, should immediately scrap calculus and instead focus on these miraculous new tools. But it is obvious now! You may never need to know how a linked list works, but if you’re reading this, you’re using a profusion of them right now. And that’s esoteric computer science mumbo jumbo that may or may not be useful. The starkly obvious realworld potential utility of computers that goes untapped because of a lack of education is pathological.

Philosophy/Ethics  A common justification for calculus (here’s one) is that it helps "teach people to think", including logic, problem solving, etc. I believe that if we have to disguise the study of philosophy as calculus (Newton and Leibniz did the reverse by the way) then that itself is terrible philosophy and proof that we have a problem. Just teach philosophy! It’s worth it!
Just as we have stopped beating kids with the lash (not sure about Texas), sometimes a society needs to accept that it’s on the wrong track and abandon the cultural script that mindlessly proscribes suboptimal practices. Although there is gathering momentum for calculus reform, by speaking out against this educational hazing I’m doing what I can to break with our obsolete past. In an ideal world everyone would learn calculus  right after the thousand other worthier subjects.
Update 20180511
I just discovered ComputerBased Math which seems like a Wolfram family project. Here’s a talk by Conrad Wolfram about how weirdly out of touch today’s math education is. His vision is slightly different than mine, but we both are in complete agreement that the current way math is taught is absurd.