"When am I ever going to use this?!?!"
Often followed by "I'm gonna be a basketball star!" or "...rock star!"" or "...novelist!"
I have seen suggestions that you're only forced into this stuff in school to exercise your brain. Or for torture.
This whole line of questioning and thinking really bugs me, and has for decades. Naturally, I wasn't 'in the room' when the folks who made the scholastic curriculum did so, so I don't actually KNOW why they put these courses in our way through K-12, but I've got what I think are some pretty iron-clad thoughts on the subject...
Let's start with the most basic, fundamental, and shallow thought: the reason that you whiners need to take algebra (for instance...could be physics or geometry) is the same reason that I had to take friggin' ART class (and music class). As I mention above, I don't actually know what the reason is, but these points are opposite sides of the same reason.
Trying to teach a kid like who I was music and art is like trying to teach rain to fall up. I have never been able to hear individual sounds in the aggregate (like hearing the flute in the orchestra), and I don't have an artistic bone in my body. I can't even draw a straight line when I have a ruler (I know: art seldom requires straight lines...my point is that I've never been able to make an image in my mind come out of the end of a pencil; I'm going to leave it to you to extend the metaphor).
The next reason in my mind is that when you tell me, "...I'm gonna be a fillintheblank!", you don't actually know that. Remember, we're talking about high school kids for the most part: those folks in the prime of their life who know the full contents of the internet (what used to be the encyclopedia, dictionary, & atlases combined), have the wisdom of the ages, and can see their own future with crystal clarity.
Here's some wisdom from the curmudgeon: you DON'T know everything. You CAN'T see your own future. While perhaps you won't ever NEED these motes of knowledge, you can never tell when they might be USEFUL. You might just find someday that knowing a bit of geometry will enable you to identify when a carpenter or carpet salesman is trying to soak you for more money than a job is worth, and unless you're made out of money, those extra few hundred or thousand dollars could actually make a difference in your life.
And on the sports angle, let's take the NFL and do a tiny bit of math: 32 teams with 65 players each is 2,080 individual players in the NFL. Add the practice squads, I'll estimate 4,000 men in the USA who make a living playing football in the NFL. Childstats.gov says there are 76.1 million school-aged children in the USA. Basic interpolation suggests that one third of these are in high school: 25.37 million kids in high school.
Half of these are boys: 12.185 million.
Wild Ass Guess: 6 million are healthy enough to be playing sports, 3 million are playing football.
3 million football playing high school boys, working for 4,000 spots: 1 in 750 of you are going to actually play professional football in the USA. Not bad odds, really...better than I thought when I started that math, BUT, this assumes that you're not hurt on your way to the NFL. Physical injury is a real probability there. I think that this basic analysis applies to all sports-minded students, and I guess my council is: have a back-up plan.
What I think is the ACTUAL reason you need to take those classes is pretty simple: exposure. It's important to expose everyone to math, science, art, literature, music, philosophy, wood working (and other industrial arts), language (starting with Latin), history, politics, writing, sports, and all the other topics that increase our awareness of the universe around us.
For one thing, if you're never exposed to a subject, how could you ever possibly know whether you've got any talents in that subject, or whether you'd like to pursue it? If you never took an art class, you might never know that you're good at it, and you might never meet your muse. Should you never meet your muse, you'll never been truly brilliant, successful, or even happy.
It may well be that you find that you enjoy math or biology, but if you didn't have those classes in school, you'd never know, and you'd miss that boat. Can you say, "You want fries with that?"?
Between the age of 5 or so until you're 18 - 13 short years (in retrospect, of course), you have to be exposed to a sufficient depth of all of these subjects to arm yourself with enough knowledge and experience to be able to make some decisions that are going to affect the entire rest of your life. AND are bound to affect the lives of your life partner as well as any kids that you might end up with and parents that might eventually have to depend upon you.
We have to be exposed to a little of everything in those few years. And they are not full years, either! In the USA, kids go to school for a total of 180 days per year, on average, which is close enough to half of the year to say that the 13 years mentioned above is actually more like 6.5 years. Not a lot, really.
In my mind, it's all about exposure.
Finally, don't fool yourself too well about never needing whatever subject it is that you're lamenting. If you ever DO get to be that professional sports star, you should know that the sporting world is full of statistics, which is math. Your contracts are going to be chock-full of math, in the form of money. If you can't do basic math, you're going to have to leave that to your agent, and you're kidding yourself if you think that your agent has only your best interests at heart.
If you ever take an interest in DIY projects, geometry is going to be your friend.
Will you NEED the knowledge that comes out of those "useless" classes? No, not necessarily, but you'll be surprised where that knowledge might come in useful.