Teenagers around the US do not as a rule have convenient access to contraceptive pills. That's because the FDA refuses to approve them for OTC sale, despite their safety relative to many other OTC meds. The stated reason for refusing OTC sales is that allowing them would prevent women from seeing their doctors for other medical issues (this is also the reason you can't buy extremely useful and safe meds like Ondansetron OTC). I feel like I'm on firm ground when I add that this is unlikely to be the only reason you can't buy OTC contraceptive pills.
Meanwhile, about half of US states require parental consent for most minors before doctors can issue prescriptions for birth control.
As a fun additional wrinkle, churches, and in particular the Catholic church, run some of the largest hospital and health chains in US metro areas. Church-run hospitals routinely refuse to provide access to contraceptive services. In Chicago, the Loyola health system --- an otherwise well-regarded health services chain! --- won't prescribe contraceptive pills to adults even for non-contraceptive reproductive health purposes!
I don't think we need to spend too much time talking about Planned Parenthood clinics; the issues there are obvious to anyone familiar with the state of reproductive health in the US.
So, no, I don't think it's reasonable to argue that any teenaged girl in the US should be expected to be fully armed with all the tools of modern contraception.
You're also giving teenagers a pass for having unprotected sex as if they don't know there's a risk of 1) getting pregnant and 2) getting an STD.
Certainly some birth control measures are less accessible to teenagers, but what I'm arguing is the parent's claim that "The vast majority of teenage mothers in the United States do not choose to get pregnant"
That's not accurate unless what is meant is that "the vast majority of teenage mothers don't want to get pregnant (but choose to forego readily available birth control / condoms)". I'd believe that.
It's common knowledge how reproduction works. You have condoms, birth control pills and copper rings among other options.
That's simply not a reasonable argument. Don't move the goalposts now.
If you don't use a condom no matter what age you are and get an STD - same thing - that's on you too.
Your argument about post-conception options - I agree that not everyone has the same access. But I'm not talking about that.
Condoms work. Teenagers know the risk. They're just being dumb and it's on them.
Now - your argument that making birth control more available - sure I think that's a good thing too. But the notion that "the vast majority of teenage mothers in the United States do not choose to get pregnant" is irresponsible because almost all of them got pregnant by being wreckless while viable options are readily available. Specifically condoms.
(The comment I just replied to was edited extensively after I replied to it. That's OK; I said what I wanted to say.)
Under those circumstances, it's not surprising that teenagers have sex, don't know how to do so safely, and end up pregnant without meaning to. That is: a teenager absolutely can choose to have sex without choosing to get pregnant, simply because the society around them has conspired to make sure they don't understand how one leads to the other.
It's strategic: prevent women from accessing the tools and knowledge to keep themselves safe, then justify denying them rights "to keep them safe."
Things could be better, of course, and that's worth talking about, but your argument has turned into a caricature.
You also have minimal->zero private money and come from a poor background so it's too expensive. Your parents are religious and it's difficult to privately have & use birth control. Copper IUDs create pretty bad periods and are more painful to insert if you never given birth. Giving yourself a megadose of hormones with other implants is pretty freaky.
But your 16 years old and have a lot of hormones...
That is part of the reason why the entire obamacare free birth control fight was pretty emotional in the USA.